请简述苯乙烯精馏塔停车后的保护方法。
参考答案:
a.塔内件可能在停车期间发生较大的腐蚀问题。
b.薄钢材料很容易被氧化,应立即通入氮气将塔内湿空气驱赶出去。
一元二次方程x2-x=1的根的情况是( )
A.有两个相等的实数根
B.有两个不相等的实数根
C.有一个实数根为1
D.没有实数根
The short-run supply curve for a firm under perfect competition:()
A. is its average variable cost curve.
B. is its average variable cost curve above marginal revenue.
C. is its marginal cost curve above average variable cost.