When he entered the room, somebody would ask him how a camera worked.

当他走进房间时，有人会问他照相机的工作原理是怎样的。

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But Pavlov observed that when somebody entered the room who typically gave him the food powder, the dog--the food powder saliva would start to come out.

他注意到,当给它喂食的人,进屋时，狗便开始分泌唾液。

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