系统的接地宜采用一点接地方式，不得形成封闭回路，不得与强电的电网零线短接或混接。（）
参考答案：对
胶带成本占皮带机成本的（）左右。
A.50%；
B.60%；
C.40%；
D.30%。
Accounting profit is often an unsatisfactory performance measure from an economic point of view because it:（）
A. does not consider depreciation.
B. does not consider the opportunity costs of equity capital.
C. considers marginal costs rather than average costs.
