Which of the following are single-celled organisms?

The correct options are
B

Amoeba

C

Chlamydomonas

D

Paramecium

Unicellular organisms, such as amoeba, paramoecium, yeast, etc., consist of a single cell. All the vital processes such as nutrition, digestion, excretion, reproduction, etc., are carried out by the single cell. Hydra, on the other hand, is an organism that is made up of multiple cells.