—Everybody is going to climb the mountain. Can I go too, mom?

—________ Wait till you are old enough, dear.[ ]

A. Will you?  

B. Why not?

C. I hope so.  

D. I'm afraid not.

_______ solids expand much less than liquids or gases, the continuous increases can add up to a lot, …

A．Although

B．If

C．Because

D．After