that terrible noise, David—Oh, I forgot to tell you The new machine in the nearbyplant_____

What’s the matter with the man hanging his headthere—Well，if you ________ know, hewas caught stealing my bike.

Leaves are found _______ all kinds of trees, but they differ greatly ______ size and shape.[ ]

What are you discussing— We are discussing_______________.

My parents want to go ______ on vacation.