五列不属于间接费的取费基数的是（ ）。
A．直接费合计
B．人工费和机械费合计
C．人工费合计
D．人工费和材料费合计
参考答案：D
The skin, an ____ part of your body and its largest organ, ____ as a barrier against diseases. [ ]
A. vital, acting
B. vital, acts
C. essential, acting
D. essential, acts
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