Combine each pair of sentences, using a relative pronoun. Put the comma(s) where necessary.
1.Nelson became president of south africa. he was in prison for 27 years.
2. john lemmon was one of the batlle. he was killed in 1990.
3. the titanic was supposed to be unsinkable. it sank in 1912.
4. queen victoria ruled over the british empire. she came to the throne in 1837.
5. oxford is often crowded in the summer. it attracts many tourists.