Final answer:
To complete the second sentence, use the word 'He' to indicate that Mr Green should not be allowed to leave.
Step-by-step explanation:
To complete the second sentence, you can use the word 'He'. So the second sentence will be: 'He must definitely not be allowed to leave.'
This sentence has a similar meaning to the first sentence because it implies that Mr Green, being a vegetarian, should not be allowed to leave for some reason. It suggests that there is a strong reason or rule in place that prevents Mr Green from leaving due to his vegetarianism.