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

Mr Smith is at the door. _______ wants to see you.

Everyone knows that _______ is dangerous to play with fire, but _______ is difficult is to prevent children from playing with fire.

He told me that he had two girl-friends, and neither of _______ knew anything about the other.

He asked a lot of questions, and none of ______ was easy to answer.

The doctor assured the patient that there was ______ with her, but she could not help worrying.

What is it _____ his daughter needs most？

Who was it _____ saved the drowning girl？

“How was ______ they discovered the entrance to the underground palace？” “Totally by chance.”

In my apartment there are two rooms, _____ is used as a living room.