当平均产量达到最大值时()。
A、总产量达到最大值
B、总产量仍处于上升阶段,还未达到最大值
C、边际产量达到最大值
D、边际产量等于零
参考答案:B
150. He was never late for school, _______ more than once by the class teacher..
A.being warned
B.after warned
C.having been warned
D.for warned
锅炉点火后应维持空冷散热器内较高背压,投入旁路前再根据低旁要求将机组背压降低到要求的数值()Kpa。