Mary ________ a smile when she heard her family went to Australia without her.

The engine of the ship was out of order and the bad weather _____ the helplessness of the crew（船员） at sea.

The question______new measures should be taken to control the terrible air pollution is______puzzles scientists a lot.

How many children have you got —Two , _______ of them are studying in the university.

We meant to finish the work by dark, but we were so tired that we could not ______.