—Sorry，Mr．Green．I have ________ my homework at home．
—Never mind．But don’t forget next time．
| A．put |
| B．kept |
| C．left |
| D．remained |
Sometimes parents find ______ hard to communicate with their children.
| A．this | B．that | C．it | D．one |
Nowadays scientists are working hard to find out ______ to do with air pollution.
| A．how | B．why | C．when | D．what |
Good teachers can usually give the students______ advice on their study.
| A．a great many | B．huge amounts of |
| C．a large number of | D．too many |
Chinese people have been using paper for over______ years.
| A．thousands | B．two thousand | C．thousands of | D．thousand |
Mother came into my study with a cup of milk in one of her hands, and an apple in ______.
| A．the others | B．other | C．the other | D．another |