The water stored in the dam on a river has potential energy.
The potential energy stored in a body of water held at a given height is converted to kinetic energy (movement energy) which is used to turn a turbine and create electricity.

Tidal energy of sea waves is harnessed by constructing hydro electric dams at the mouth of narrow bays along the sea coast.
Hence, The tidal power plants are constructed near the mouth of narrow bays.

Answer is A.

Potential energy is the energy that is stored in an object due to its position relative to some zero position. An object possesses gravitational potential energy if it is positioned at a height above (or below) the zero height.
There is potential energy stored in a water reservoir behind a dam. It is converted to kinetic energy when the water starts flowing down the penstock, from the dam. This kinetic energy is used to turn a turbine.
Hence, the source for hydro electricity power generation is potential energy of water.

To harness hyrdoelectric energy large hydroelectric plants are required to be built across the streams. These plants should be of very high qulaity and are expensive to build. Dams are not only costly but they also take a toll on the environment and natural habitat near it.

In hydro electric plants:

The water required for generation hydel power is available free of cost. Construction of dams in not an easy task. It needs heavy investment.

For running a hydel power station throughout the year, vast amount of water  is required. This demands a vast reservoir. Such a  reservoir can be made only at a few places which are geographically suitable and do not interfere with ecosystem and human habitation.

Ultimate source of hydroelectricity is the energy of sunlight (solar energy). Heat energy of the sunlight evaporates water in oceans and lakes. This evaporated water goes into the atmosphere and returns back to the Earth as rain water or snow.

The minimum height required to convent the stored potential energy of water into electric energy is $34\ M$ between the turbine and free energy of water in reservoir.

Water energy has the following advantages
a) Water energy is renewable and inexhaustible source of energy.
b) Water energy does not cause any pollution
c) Water energy is a cheap source of energy.

As the water is released through control valve, the potential energy of water changes to kinetic energy. As the water flows into reservoir from the catchment area, the kinetic energy of flowing water changes to potential energy.

The dams are constructed for the following purposes:
a) To prevent flooding of the rivers in the area.
b) To provide water for irrigation purposes.
c) To generate hydroelectricity.

Providing water to irrigation process is an advantage of creating dam.

The dams across the Rivers can disturb the aquatic life and can lead to their large scale destruction the fishes and other water animals may enter the power generation turbines where they may get crushed.

The construction of dams for generating hydro electric power and then installation of transformers and their connection to the national grid has the following four main disadvantages:

A) Disturbance of the natural ecosystem in the surrounding forest area.

B) Disruption of the plants and animals life.

C) Displacement of people on a large scale.

D) Disruption of the aquatic ecosystem.

The construction of dams for generating hydro electric power and then installation of transformers and their connection to the national grid has the following four main disadvantages:

A) disturbance of the natural ecosystem in the surrounding forest area.

B) disruption of the plants and animals life.

C) displacement of people on a large scale.

D) disruption of the aquatic ecosystem.

Potential energy is stored energy or the energy of position. The potential energy stored in a body of water held at a given height is converted to kinetic energy (movement energy) which is used to turn a turbine and create electricity.
Hence, water stored in the reservoirs of hydro-electric dams has potential energy.

The construction of dams for generating hydro electric power and then installation of transformers and their connection to the national grid has the following four main advantages:

A) disturbance of the natural ecosystem in the surrounding forest area

B) disruption of the plants and animals life

C) displacement of people on a large scale

D) disruption of the aquatic ecosystem.

So,construction of dams is not always advantageous.

Initially water is collected in the dam. When it is released, the potential energy is converted to kinetic energy. The released water is made to fall on the blades of turbines. The armature of the electric generator rotates to produce electricity.