A) can или may.
1. I ... not do this work. It is too difficult for me.
2. ... I come in?
3. We ... understand him well. His English is perfect.
4. I ... swim very well when I was a boy.
5. They … be late for the train, if they don’t hurry.
B) must/need.
1. You ... rely on this result. They are very accurate.
2. She ... an hour to write a composition.
3. You ... consult a doctor. Your illness is very dangerous.
4. Our company ... highly qualified specialists.
5. This book ... be published by all means. It is very interesting.