我们通常所说的关税壁垒是指（ ）。
A. 低额出口税
B. 高额出口税
C. 低额进出口税
D. 高额进出口税
This selection is primarily concerned with ______.
A. the eye's adaptation to color
B. the properties of colored surfaces
C. the color of colors
D. the effect of changes in color intensity
The Social Security Act did not include health insurance because the commission considered that its inclusion would jeopardize the passage of the act.
A. evade
B. endanger
C. exclude
D. enhance
将业务集中于少数国家的少数细分市场的战略称为（ ）。
A. 市场专门化战略
B. 区域集中战略
C. 多元化战略
D. 集中化战略
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