I am using dS rather than dA because I still want to think of dA as maybe the area in one of the coordinate planes like the one we had in double integrals. You will see later where this comes in.
这里使用dS而不是dA，因为我习惯把dA看成是，坐标平面中的面积元，就像在二重积分中所做的那样，待会大家会了解。
Brian : On the whole quite disappointing really. I got three Fs, two Ds and a C. But I did get one A!
布莱恩： 大致上很失望，我只拿到三个F、两个D和一个C，但我也拿到一个A！
I just hope that if there is any revision, it's at least as wide as the DS one.
我只是希望如果真的有一个新机器，他应该至少和DS差不多大小吧。
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