21.It was not until dark ____ he found ____ he thought was the correct way to slove the problem.
─Are you going to plant a great many trees in this area? ─Yes. The soil _________ away in this way.
It is known to all of us that lions ________ meat-eating animals.
These plants are watered___________
Many kinds of help ________ by plane or by train to the area ever since the earthquake hit it.
______ is announced in today’s paper, they have succeeded in solving many problems in accordance with the new theory.