When doing my homework, .
A. I heard the doorbell ring
B. the doorbell rang
C. my mother came in
D. my mother was cooking
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(答案→)A. I heard the doorbell ring
B. the doorbell rang
C. my mother came in
D. my mother was cooking
解析：考查状语从句的省略和宾语补足语：句意：当做作业的时候，我听见门铃响了。“while”后接的是现在分词短语，在句中作状语，它逻辑上的主语应该是我，不是the door，也不是my mother，又因为hear后接复合宾语时，这个复合宾语应包含一个省略to的动词不定式或现在分词短语。所以本题选A项。