What's this？

It's _______ watch．（　　）

A．aB．anC．the

Are these your books？

No， they aren't． They are _______．（　　）

A．sheB．hersC．her

Mountain climbing is one of _______ sports in the world．（　　）

A．dangerousB．more dangerous

C．the most dangerous

I cleaned my room yesterday． It _______ a little difficult．（　　）

A．isB．wasC．will be

I think it's impolite _______ others waiting．（　　）

A．to keepB．keepingC．keep