The key answer of exercise 3

a

1. defining relative clause
2. defining relative clause
3. non-defining relative clause
4. defining relative clause
5. non-defining relative clause
6. non-defining relative clause

b

1. who → defining, no. commas
2. who → non-defining, commas after 'Jim' and 'stories'
3. which → defining, no commas
4. whose → defining, no commas
5. where → defining, no commas
6. when → defining, no commas
7. which → non-defining, comma after 'Cambridge'
8. which → defining, no commas