The key answer of exercise 1

a)

Part 1

1. stop
2. arrive, exchange, move, phone
3. start, wait

Part 2

• buy → bought
• leave → left
• say → said
• see → saw
• send → sent
• sit → sat
• tell → told
• write → wrote

c)

1. say → said
2. tell → told
3. finish → finished
4. wait → waited
5. buy → bought
6. phone → phoned
7. write → wrote
8. stop → stopped
9. leave → left
10. send → sent
11. arrive → arrived
12. start → started
13. see → saw
14. sit → sat
15. ask → asked