The key answer of exercise 5

a)

1. question 3
2. question 1
3. question 5
4. question 5
5. question 4
6. question 5

b)

1. 1,3,5,6
2. 2,4
3. Students' ideas, but here are some examples → to emphasise a particular item; to make it easier for the listener to follow due to the real-time nature of speech; to manage long noun phrases more easily, by partly separating them from the main clause; because the speaker often realises they left a detail out, and want to add it on.
4. Spoken informal English

c)

1. 1, 3
2. 5, 6
3. 2, 4