输油站常用的螺杆泵多采用（）。
A.单螺杆泵
B.双螺杆泵
C.三螺杆泵
D.四螺杆泵
参考答案：C
通常金属氧化物比金属具有更高的热稳定性，脱氢反应中大多数都选用的金属氧化物为催化剂
It was not long before Skinners, the famous behaviorist, realized the limitations of his psychological research than another psychologist came with his forceful arguments against Skinners’ theory.
A. realized... when B. had realized... whenC. was realizing... then D. would realize... as
