问题描述：
while watching television,_______.1 the doorbell rang 2 we heard the doorbell ring
3 there was someone knocking at the door
4 we heard the doorbell rung
选择哪一个,及说出为什么
我最想知道的是，为什么
3 there was someone knocking at the door
4 we heard the doorbell rung
选择哪一个,及说出为什么
我最想知道的是，为什么
问题解答：
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