Correct sentence: Piranhas hunt in schools.
Why this is correct:
- We need in, not is. The word in tells where they hunt (inside a group), while is is a form of the verb "to be" and does not fit here.
- Piranhas is plural (more than one), so we use the plural verb hunt. If it were one piranha, we would say: "A piranha hunts."
- Schools means groups of fish. So "in schools" means they hunt together in groups.
Easy examples:
- One dog runs. → "A dog runs."
- Many dogs run. → "Dogs run."
- One piranha hunts. → "A piranha hunts."
- Many piranhas hunt together. → "Piranhas hunt in schools."
Tip: Use in to show place (where). Use hunt with many animals, and hunts with one animal.