Four dollars a pair? Ithink it’s a bit too much.-If you buy three pairs, the price for each will _______to three fifty.[ ]

Over the past decades, forest area ______ in China as a result of massive deforestation

It’s easy to make friends, but it’s difficult to keep the ________ longer.

The invention of the Internet has ________ a lot to the development of the world.

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