Biology is _____.

But the unpleasant feeling of coldness disappeared at the _______ of his students pouring out of their classroom to give him a warm, wordless welcome.

I can remember very few ______ when he had to cancel his plans because of poor health.

He often asks his neighbour to look after his pet during his _______.

You’d better have a talk with your friend _____, and then the misunderstanding will disappear.