the police found out one clue that voices were heard for help from some very distant place
问题描述：
the police found out one clue that voices were heard for help from some very distant place
a to call b calling 感官动词被动不是加 to do 可是答案选的是b heard后面
答
The police found out one clue that voices were heard ___ for help from some very distant place
a to call b calling
选b.
因为hear sb calling/call 变成被动形式是sb be heard doing/ to do
句意是【当时正在呼救】,所以用hear sb calling,变成被动形式是sb be heard doing.
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