Someone is at the door. ________ must be Mr Smith.

The chairman thought _____ necessary to invite Professor Smith to speak at the meeting.

Of all the clues they provided, ______ is of any help for solving the case of robbery.

I bought the train tickets at the station easily during the spring rush, though ________ of them ________ it.

I hate _______ in the winter when the weather is wet and freezing cold.