Which of these is an organism?

a

a drop of water

b

a herd of sheep

c

a heart

d

a wolf

D. Wolf

Explanation:

An organism is a living thing, like a plant or an animal. Thus, you can rule out A (because water isn't alive) and C (a heart is an organ, not an organism). That just leaves B and D. Since the questions is asking for a singular organism, the answer must be D (a wolf).