2.      They caught the elephant again.

’ The elephant was caught again.

3.      She bought the watch at the shop.

’ The watch was bought at the shop.

4.      They built the house in 1950.

’ The house was built in 1950.

5.      We did the exercises last week.

’ Exercises were done last week.

6.      The pupils sent the letters the day before yesterday.

’ The letters were sent by the pupils the day before yesterday.