Example key:
1 The man who is running after the burglar, has grey hair and a moustache.
2 The thief, who has stolen the vase, is looking over his shoulder.
3 The man whose vase has been stolen, is running after the burglar.
4 The vase which the burglar is carrying is expensive.
5 The whistle on which the policeman is blowing, makes a lot of noise.
6 The burglar after whom they all are running, is going to fall.