题目内容
The new system needs to be in operation for five months ________ it can be updated.
| A.as | B.while |
| C.before | D.once |
C
C考察状语从句。本句的before用语肯定句中,强调主句动作持续的时间比较长,意为:要多多久….才。故C正确。
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题目内容
| A.as | B.while |
| C.before | D.once |