The correct options are
A Amoeba
B Spirogyra
C Paramoecium
D Chlamydomonas
Amoeba, paramoecium, chlamydomonas, spirogyra etc., are all single-celled or unicellular organisms.
In these, the single cell is capable of performing all the life processes like obtaining food, respiration, excretion, growth and reproduction.