QUES:
Who is they in the following sentence?

Horses are faster at short distances than camels, but they cannot trek as far.

ANS:
Horses

QUES:
Who is it in the following sentence?

The sword was stuck in the tree because it was wedged in there really well.

ANS:
The sword

QUES:
Who is it in the following sentence?

The knife cut through the fence because it was sharp.

ANS:
The knife