Are they all possible?

[dilodi83]

A1) a herd of elephants
2) a flock of elephants

B1) a herd of sheeps
2) a flock of sheeps

C1) a herd of people
2) a flock of people

D
How it uses its trunk to pull up a ...........(spot, tuft, mouthful) of grass to eat... ARE THESE THREE NOUNS POSSIBLE IN THIS CONTEXT?

[bhaisahab]

A1) a herd of elephants Yes.
2) a flock of elephants No.

B1) a herd of sheep No.
2) a flock of sheep Yes.

C1) a herd of people No.
2) a flock of people No.

D
How it uses its trunk to pull up a ...........(spot, tuft, mouthful) of grass to eat... ARE THESE THREE NOUNS POSSIBLE IN THIS CONTEXT?

"Tuft" and "mouthful" are OK, "spot" is not.

[Barb_D]

Agreed, but with two comments:

You can use a herd of people to speak metaphorically. It's not normal usage, but if you want to describe a scene and make it seem as though the people were moving (or being moved about) as though they were cattle, you could use herd.

Flock is applied to people in a church setting sometimes, as though the minister were the shepherd and the congregation his flock.

[Tdol]

You can also have a memory of elephants or a parade of elephants: Fun With Words: Collective Nouns