Computers in offices and homes since 1970s．
| A．have been used | B．had been used | C．was | D．has been used |
The mixture of his improved self-confidence and never-ending efforts is ________ lies behind his rapid progress in his study.
| A．what | B．that | C．where | D．which |
Taking a gap year is a good chance for students to learn skills and gain life experience, ______ them an edge in the job market.
| A．given | B．to give | C．giving | D．having given |
If you________ the failed experiences, you would not havemade such a mistake in your homework.
| A．refer to | B．have referred to |
| C．referred to | D．had referred to |
Humor, if ________ properly, will help us break the ice and gain affection of others in social communication.
| A．using | B．used | C．to use | D．to be used |
I can't tolerate being made fun of，________never to come again.
| A．determined | B．being determined |
| C．determine | D．to determine |