All natural minerals contain _____.
A. impurity
B. impurities
C. impure
D. impures
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Job losses are an unfortunate _____ of the recession.
A. byproduct
B. product
C. result
D. outcome
Additives are expensive but are used in very low ____.
A. concentration
B. concentrations
C. percent
D. contain
The choir stood in four rows according to their ____ heights.
A. respectable
B. respectful
C. respective
D. respected
制动盘加工时,加工了
A. 内孔
B. 端面
C. 螺纹孔
D. 退刀槽