Assume that a company has equal amounts of debt, common stock, and preferred stock. An increase in the corporate tax rate of a firm will cause its weighted average cost of capital (WACC) to:（）

A. rise.

B. remain the same.

C. fall.

氮气置换管线的说法正确的是（）。

A、置换合格的标准是：氧含量不大于1%

B、操作人员应站在排放口的上风口，避免危险

C、充氮压力不允许管线设备的设计压力

D、充氮压力不应超过PSV放空压力