The doctor said jokingly that his own infection of the virus _______ the discovery of a vaccine (疫苗)of the disease.
| A．stood for | B．called for | C．paid for | D．contributed to |
We all consider ______ important that we should put theory into practice.
| A．that | B．which | C．this | D．it |
Just like fingerprints, each person’s DNA is ________unless he has a twin.
| A．unusual | B．normal | C．various | D．unique |
The boy felt quite happy because he was closer now to ______ an answer of his own.
| A．have found | B．find | C．finding | D．having found |
Taking charge of the big company, I’m afraid, is _____ his ability.
| A．beyond | B．within | C．of | D．to |
When the fire________，the people in the building lost their head and ran in all directions.
| A．broke in | B．broke away | C．broke out | D．broke down |