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

Our city has changed a lot; who can tell what it will be like in _____ten years?  

---He found a baby in his car when he came back from the supermarket. And         was crying for some milk. --- When was        ?---      was in 2000 when he was still in college. 

You can choose _____book you like in the library.

In American there are more households(户主) with pets than ____ with children.