The problem is _____ has caused us a lot of trouble.
As you are now a member of our society we shall let you ____ our secrets.
__ many times, but she still didn't know how to do it.
Scientists think that the continents ____ always where they ___today.
--- Would you tell me ___ you want your tea, with sugar or milk?--- Sugar, please.
Leaves are found on all kinds of trees, but they differ greatly __ size and shape.