题目

We had just covered half the journey________the engine failed and we could do nothing but wait for help. A．before　                              B．since C．when　                                D．until 答案：C 解析：　句意为：我们刚走了一半这时发动机就出故障了，我们别无选择只能等着救援到来。when就在这时；突然……。before在……之前；since自从；既然；until直到。

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