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Till then, John ( ） from his sister for about half a year.
A、hadn't heard
B、didn't hear
C、hasn't heard
D、won't have heard
【正确答案】：A
【题目解析】：till then 到那时为止，主句的谓语动词发生在then 之前，过去的过去，因此用过去完成时，句子含义是，到那时为止，约翰大半年没有收到他姐姐的来信。