Deforestation is the removal of a forest or stand of trees where the land is thereafter converted to a non-forest use. Examples of deforestation include conversion of forestland to farms, ranches, or urban use. So, the correct answer is option C.

The deforestation greatly effects on the environment. Plants absorb CO$ _2$ from the atmosphere to perform photosynthesis. If plants are destroyed, then the level of CO$ _2$ in the atmosphere will rise. As a result, CO$ _2$ will trap more heat radiations, thereby adding to global warming. An increase in the temperature of the Earth will disturb the natural water cycle. As a result, there will be a change in the rainfall pattern. This could lead to floods or droughts.

In India, deforestation is the main cause of soil erosion. The quality of topsoil loss in India is about 18.5% of the total global loss.

As the population increases, the need for land also increases, forests are cleared for the construction of roads and malls and buildings. The demand of food grains also increases, so it calls for clearing more trees and growing food crops. Forest fires also cause deforestation.

Forest fires are naturally caused and not man made like urbanization and agricultural activities, hence, they are the only natural cause of deforestation. Natural fires are caused by lightning, with a very small percentage started by spontaneous combustion of dry fuel such as sawdust and leaves. Human activities may also lead to forest fire.

Deforestation means cutting down of forests. Droughts are natural causes of deforestation and urbanization is the man-made cause of deforestation. The most dramatic impact is a loss of habitat for millions of species. Seventy percent of Earth's land animals and plants live in forests, and many cannot survive the deforestation that destroys their homes.

Natural causes of deforestation are forest fires, droughts, exotic animals, floods, climate change, and overpopulation of foreign animals. All of these add to deforestation. Forest fires burn trees in large amounts. Many animals depend on trees for shelter. When a drought occurs, trees won’t have water to survive, also leaving animals without a stable home. Also, when animals that are not from the area come and make it their habitat, they take food, water and space up that need to be used by native animals. 

Deforestation is the permanent clearing of forests to make the land available for other uses. The main reasons for deforestation are overpopulation, urbanization, wood requirement, obtaining land for cattle-grazing. There has been a considerable decrease in the number of plant and animal species due to deforestation.  Other ill-effects are rise in pollution, global warming and soil erosion. Thus the correct answer is option D.

the correct answer is 'all of the above'

Cash crop economy of third world is a cause of deforestation is not true for deforestation rest all options  are the reasons for deforestation.

Deforestation and combustion of fuel increase the concentration of carbon dioxide in the atmosphere. Deforestation is the excessive cutting down of trees which increases the carbon dioxide concentration in the atmosphere. Fuels burns in the atmosphere in the presence of oxygen. Burning of fuel in the sufficient supply of oxygen leads to the production of carbon dioxide while the insufficient supply of oxygen leads to the production of carbon monoxide.

Answer is option D i.e. "All of the above"
Deforestation(disappearance of the forest) is when humans remove or clear large areas of forest lands and related ecosystems for non-forest use.

• Without trees, rain runs off soil into rivers and streams i.e soil erosion, raising the water level which leads to floods.
• When deforestation takes place it results in an increase in carbon dioxide concentration in the atmosphere which results in global warming.
• If forests are destroyed, animals and other creatures of the forests will come out to human settlements searching for a place to stay. They will be killed more, thus leading to their extinction.

Trees in general are known as 'lungs of Earth' because they absorb large amounts of carbon dioxide and release large amounts of oxygen due to photosynthesis. This helps maintain a balance between the proportion of oxygen and carbon dioxide in the atmosphere as the oxygen released by the plants during photosynthesis is utilized by various organisms including plants for respiration.

Destruction of forest cover is called as deforestation. An important anti-forest measure is clearing forest. Important reasons for deforestation are a land requirement for cultivation, hydroelectric projects, human settlements, the requirement of wood and timber, mining and quarrying etc.

cutting down trees reverses the effects of carbon sequestration and releases greenhouse gases (including carbon dioxide) into the atmosphere. Deforestation changes the landscape and reflectivity of earth's surface, i.e. decreasing albedo.

• Plants provide shelter for animals and they make oxygen for the animals to live. When animals die they decompose and become natural fertilizer plants. Plants depend on animals for nutrients, pollination and seed dispersal. 
• Hence Plants and animals in the forest are dependent on one another.
• Hence the given statement Plants and animals in the forest are not dependent on one another is a wrong statement.
• So, the correct answer is 'Option D'.

Waldsterben refers to the mass death of the trees wherein, the peripheral parts of the plants are killed and slowly the entire forest population dwindles. It was first reported in Germany in the early 1980s. The atmospheric pollution was the main cause of such deaths of trees. Tropospheric ozone is the secondary pollutant. Nitrogen oxides and sulphur oxides are released by the industrial emissions and vehicular exhausts. Acid rain is the chemical reaction between these oxides and water to form their respective acids that precipitate with the rains. The pollutants have severe effects on the trees.

Deforestation is excessive cutting of the trees. it clears the land area which can cause the floods or may lead to infertility of the land. The most dramatic impact is a loss of habitat for millions of species. Seventy percent of Earth's land animals and plants live in forests, and many cannot survive the deforestation that destroys their homes.

Deforestation leads to the increased percentage of carbon dioxide components of the environment because trees provide oxygen by taking up carbon dioxide when their number reduces the carbon dioxide was unable to be converted into oxygen. That's why its components increases.

• Trees help keep soil in place by holding a large amount of soil with there roots.
• Without trees, rain runs off soil into rivers and streams, raising the water level which leads to floods.
  
• Planting trees acts to shield soil from the winds, and the mulch from fallen leaves forms a layer to protect the soil on the "forest" floor.
  
• Hence the forest helps the soil to prevent the flood.
• So, the correct answer is 'Forest'.

• Deforestation is when humans remove or clear large areas of forest lands and related ecosystems for non-forest use. These include clearing for farming purposes, ranching, and urban use. In these cases, trees are never re-planted.
• Plants absorb large amounts of carbon dioxide from the atmosphere. When deforestation takes place it results in an increase in carbon dioxide concentration in the atmosphere which results in global warming.
• Without trees, rain runs off soil into rivers and streams, raising the water level which leads to floods. Hence deforestation results in the flood.
  
• Deforestation also results in the extinction of flora and fauna(plants and animals).
• Hence The consequences of deforestation are  Global warming, Flood and Extinction of flora and fauna.
• So, the correct answer is 'All the above'.

• Forest is also called the Lung of Earth because they absorb a large amount of carbon dioxide from the atmosphere and release oxygen into the atmosphere.
• The Amazon rainforest functions as a giant air machine that absorbs a large amount of carbon dioxide, and produces oxygen. More than 20 per cent of the world oxygen is produced in the Amazon Rainforest. 
  
• Hence Forest is also called a Lung of Earth.
• So, the correct answer is 'Lung of Earth'.