1. Directions: Complete the sentences with appropriate relative adverbs or "prep. + which /whom".

1. （1） There are occasions animals might detect earthquakes before they occur.
3. （2） The various means plants resist insect attacks are to be classified and discussed.
5. （3） The chimpanzees have been getting sick because of people's diseases since people entered the forests they live.
7. （4） Some people think that the main reason animals are kept in zoos is to protect some endangered and valuable species.