The boy was often heard ___ happily in the room.
A. sing B. to sing C. singing D.sings
有人认为因句中的often,所以是听到唱歌的全部过程,所以选择B.
但是我觉得C. singing也可以。经常听到不完整事件也符合逻辑呀。下面句子摘自牛津:
You can often see people dealing openly on the streets.
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