John in his room when he heard screaming.A. is studyingB. studiedC. was studyingD. has st

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A. is studying
B. studied
(答案→)C. was studying
D. has studied
解析：重点理解句意，从而判断时态的选择。句意：当约翰听见尖叫声时，他正在他的房子里学习。从when所引导的时间状语从句看，动作发生在过去，可知句子要用过去进行时，表示过去某个时间正在做某事。