Thallophytes lack differentiation of plant body into the stem and leaves. The plant body is called as a thallus. They lack vascular tissue, the sex organs are unicellular and when multicellular, all are fertile. Thus, the correct answer is option D.

The term Thallophyta was coined by Endlicher. The organisms included in Thallophyta are algae, fungi, slime mould and bacteria.
Linneaus gave biological classification.
Hackel contributed in the history of evolutionary theory. He proposed a link between ontogeny and phylogeny.
Christensen contributed in physics in diagnostic radiology.

Fucoxanthin is a xanthophyll, with formula CHO. It is found as an accessory pigment in the chloroplasts of brown algae and most other heterokonts, giving them a brown or olive-green color. It is the principal pigment of Phaeophyceae.
Phycocyanin is a pigment-protein complex from the light-harvesting phycobiliprotein family, along with allophycocyanin and phycoerythrin. It is an accessory pigment to chlorophyll. All phycobiliproteins are water-soluble, so they cannot exist within the membrane-like carotenoids. 

Pond silk is the common name of Spirogyra (algae) because it is very slimy.
Spirogyra is a  genus (about 400 species) of freshwater green algae which are found in shallow ponds, ditches and amongst vegetation at the edges of large lakes, generally growing free-floating.
Cells are joined end-to-end in an unbranched, largely unspecialised, stiff filament and are cylindrical with one or two spirally-wound chloroplasts on which many pyrenoids are borne. The cell wall is of two layers, the outer of cellulose and the inner of pectin. Filaments can be several centimeters in length. It generally has a rather silky feel and a shiny green colour.

Cryptogamae means hidden reproduction, referring to the fact that no seed is produced, thus cryptogams represent the non-seed bearing plants. A cryptogam is a plant that reproduces by spores, without flowers or seeds. 

Ulothrix being an haploid organism, shows zygotic meiosis. Zygote is the only diploid structure which undergoes meiosis to form four cells. Each develops into Ulothrix.

Ulothrix is an example of division Thallophyta, while Funaria and Riccia are example of Bryophyta and Adiantum is an example of Pteridophyta. 

Stigeoclonium shows heterogeneous habit which differentiated into prostrate and erect system.

Non flowering plants are those plants which cannot produce flowers. They reproduce mainly through spores. Examples of non flowering plants include ferns, mosses and liverworts. They belong to cryptogams. Cryptogams are non flowering and seedless, spore-bearing plants. 

Chara is a streptophytic algae that grows underwater. It does not produce flowers and remains in a submerged stage.

Litmus solution is a purple dye, which is extracted from lichen, a plant belonging to the division Thallophyta, and is commonly used as an indicator. 
There are many other natural materials like red cabbage leaves, turmeric, coloured petals of some flowers such as Hydrangea, Petunia and Geranium, which indicate the presence of acid or base in a solution. These are called acid-base indicators or sometimes simply indicators.

Thallophyta: salient features are- most primitive and simple plants. They do not possess a vascular system. The plant body is not differentiated into stem roots and leaves. The whole plant body remains in the form of an undivided mass of cells called thallus. The mode of nutrition is photosynthetic, parasitic or saprophytic. They reproduce both sexually and asexually. Asexual reproduction usually reproduction takes place by spore formation. Fertilization is not followed by embryo formation. The division Thallophyta includes two major classes, algae and lichens. 

The eyespot or stigma is a photoreceptive organelle found in the flagellate of green algae like Chlamydomonas and some other unicellular photosynthetic organisms such as euglenoids. It allows the cells to sense light direction and intensity and respond to it by swimming either towards the light (positive phototaxis) or away from the light (negative phototaxis). A related response occurs when cells are briefly exposed to high light intensity, causing the cell to stop, briefly swim backward, then change swimming direction. Eyespot-mediated light perception helps the cells in finding an environment with optimal light conditions for photosynthesis. Eyespots are the simplest and most common "eyes" found in nature, composed of photoreceptors and areas of bright orange-red pigment granules. Signals relayed from the eyespot photoreceptors result in alteration of the beating pattern of the flagella, generating a phototactic response.

Green algae have chloroplasts that contain chlorophyll a and b, giving them a bright green color, as well as the accessory pigments beta carotene and xanthophylls, in stacked thylakoids. The cell walls of green algae usually contain cellulose, and they store carbohydrate in the form of starch. The end products of photosynthesis in these green algae are starch and proteins.

The plant body consists of unbranched, uniseriate filaments. The cells of the filaments are arranged end to end. They are barrel-shaped or cylindrical in shape. The apical cell is somewhat rounded at its terminal end whereas, the basal cell is elongated and does not have chlorophyll. It is also called as the basal holdfast, which attaches the filament to the substratum.

During the process of photosynthesis, phytoplankton produces oxygen as a byproduct. Due to their vast and widespread populations, algae and cyanobacteria are responsible for approximately half of all the oxygen found in the ocean and in our atmosphere. During day time they float, due to the accumulation of oxygen. Whereas the reverse happens during the night, which is explained below.
In addition to providing food and oxygen for nearly all life on Earth, phytoplankton help to regulate inorganic carbon (carbon dioxide) in the atmosphere. During photosynthesis, carbon dioxide and water molecules are used to make sugar for energy. The process of incorporating inorganic carbon into organic carbon (glucose and other biologically useful compounds) is called carbon fixation and is part of the biological carbon pump.
As carbon fixation and oxygen production are part of the same process, the extent of phytoplanktons participation is on the same scale. Phytoplankton consumes a similar amount of carbon dioxide as all land plants combined. While phytoplankton can pull carbon dioxide from the atmosphere or the ocean, it will have a similar effect. Carbon dioxide that is taken from the water is replaced by carbon dioxide from the atmosphere.