单选题
If no one ______ the phone, they must have gone out for breakfast.
A、
answer
B、
answered
C、
had answered
D、
has answered
【正确答案】
B
【答案解析】
[解析] 由if引导的虚拟条件句表示假设，动词用过去时。故本题答案为B。
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