When I tried to find _________that prevented so many people from taking part in the program, it seemed to me that there were two main reasons.
A．why it did
B．that it did
C．what it was
D．why it was
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—What happened ________Sarah?
—She failed in the English test.
A．to
B．with
C．in
D．on
车轮的蛇行运动和车轮的（）有关。
A、锥度
B、圆柱度
C、粗糙度
（）主要用于量取体积要求不太精确的液体。
A、量筒
B、烧杯
C、容量瓶
D、移液管
X线穿过人体后，强度分布出现差异，称为
A．物体对比度
B．X线对比度
C．天然对比度
D．吸收对比度
E．影像对比度
什么是火险隐患？