A fourth-grade teacher was giving her pupils a lesson on logic.

小学四年级的教师正在给学生们上一堂逻辑课。

Here is the situation， she said. A man is standing up in a boat in the middle of a river， fishing. He loses his balance， falls in， and begins splashing and yelling for help.

她举了这么一个例子：有这样一种情况，一

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