Complete the sentences with the correct passive form of the verbs in brackets.

1. All tourists........ (warn) to leave the beach when there's a red flag.
2. The children............ (not teach) in the villages where they live.
3. This photo............. (take) when we were in India.
4. More help........ (need) if we are going to change this situation.
5. The rubbish bags.......... (collect) earlier this morning.
6. Dangerous animals............. (not use) in the documentary we saw.
7. The river........... (clean) by volunteers every year.
8. Those small houses............ (build) by our grandparents many years ago.