26. Did you hear about the earthquake? It occurred in California

=> Did you hear about the earthquake which occured in California?

27. A river is not safe for swimming. It is polluted

=> A river which is polluted is not safe for swimming.

28. The doctor was very gentle. He examined the sick child

=> The doctor who examined the sick child was very gentle.

29. The man is standing over there. I was telling you about him

=> I was telling you about him who is standing over there.

30. The meeting was interesting. I went to it

=> The meeting where I went to was interesting.