______ is known to everybody that the moon travels around the earth once every month.
| A．It | B．As | C．That | D．What |
We must show concern ______ each other.
| A．with | B．for | C．at | D．to |
I ______ too much reading.
| A．am tiring | B．tired out because of | C．am tired out in | D．tired myself out with |
We hope that she will _____soon.
| A．returns back | B．reach to home | C．reach for | D．pull through |
If we can keep _____ this speed, we'll arrive there in two or three hours.
| A．on | B．to | C．up | D．at |
The Great Wall was built to keep ______ the invaders.
| A．in | B．out | C．up | D．off |