He is standing in front of the blackboard, his back towards us.
他站在黑板面前，背对着我们。
Now, turn round, face the back without looking at the blackboard.
现在转身面对后面，不要看黑板。
He left the minute you turned back to write on the blackboard.
当你一转身到黑板上写字时，他就溜走了。
There is a blackboard at the back of the classroom.
教室的后面有一块黑板。
There is a blackboard at the back of the classroom.
教室的后面有一块黑板。
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