Mum, my trousers are old. I want to buy a new ______

1. A.
   one
2. B.
   trousers
3. C.
   pair
4. D.
   it

Mum, my trousers are old. I want to buy a new ______.

— Mum, my friends are waiting for me outside. May I go out to play with them?

— Yes, you        , but be careful, please.

A．shall             B．must             C．may              D．should