I will have begun to do the work ______ 3 o’clock this afternoon.

It is necessary to explain your theory _____, otherwise the   audience won't make sense of what you are trying to get across.

  You’ve been so kind to us that we will always be deeply _____.

If you are too formal, people around you won’t be  __________.

 —More than fifty students competed _______each other in the composition competition. —But they could only compete _______three medals.