Listen! There is a knock on the door．Who _____ it be?—It must be Jack．Just now I sent for him．

You should your teacher’s advice if you want to improve your science.— That sounds great.

There is something wrong ___my bike. [ ]

I hear that Lily’s brother is a worker here.—Look! The manis working over there is her brother.

, I think, and all the problems could be settled.