The boy is often found _____in reading books.
| A．absorbs | B．is absorbed | C．absorbing | D．absorbed |
_______ the Atlantic Ocean crosses the equator, the trade winds cause a flow of water to the west.
| A．That | B．When |
| C．Where | D．Though |
To enjoy the scenery,Irene would rather spend long hours on the train _______ travel by air.
| A．as | B．to |
| C．than | D．while |
The pianist waited for silence a while _______ he began to play the violin.
| A．until | B．when |
| C．after | D．before |
Scientists say it may be five or six years _______ it is possible to test this medicine on human patients.
| A．since | B．after |
| C．before | D．when |
It was some time _______ we realized the truth.
| A．when | B．until |
| C．since | D．before |