A、fh=∑h
B、fh=∑-<img src="https://img.ppkao.com/2015-10/liuziyi/2015102808551524421.jpg">(<img src="https://img.ppkao.com/2015-10/liuziyi/2015102808551312142.jpg">-<img src="https://img.ppkao.com/2015-10/liuziyi/2015102808551451754.jpg">)
C、fh=∑<img src="https://img.ppkao.com/2015-10/liuziyi/2015102808551715419.jpg">-∑<img src="https://img.ppkao.com/2015-10/liuziyi/2015102808551817163.jpg">
D、∑h=∑a-∑b
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