People have become aware ______the fact that carbon dioxide, poison to the environment, contributes_____ air pollution.
| A．of, to | B．/, to | C．of, of | D．of, for |
The reason _______ he raised for being late with the exercise was ______he had to send his mother to school.
| A．that, that | B．why, because | C．why, that | D．that, because |
It is said _________ was how Chinese characters developed.
| A．that | B．that which | C．that that | D．what |
The coin was almost worthless. So it was of small ________.
| A．honour | B．quality | C．value | D．price |
She had hardly got back to the kitchen ________ the doorbell rang.
| A．when | B．than | C．as | D．as soon as |
They discovered the cause of the fire accidentally. They discovered it _______.
| A．fortunately | B．by chance | C．all of a sudden | D．on purpose |