阿拉巴马州和密西西比州有差不多一半的孩子没有达到数学考试的及格线，这意味简单的加减乘除也会令他们够呛。
In Alabama and Mississippi nearly half of them score "below basic" on maths, which means that even simple calculations baffle them.
从数学意义上来说，这是dx部分加上dy部分的线积分。
On the math it is a line integral of something dx plus something dy.
只不过物理上的解释大相径庭，但对于数学家来说，它们是两种建立过程和计算办法都一样的线积分。
Just the physical interpretations will be very different, but for a mathematician these are two line integrals that you set up and compute in pretty much the same way.
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