题目：
Specific duties are levied ______ some physical unit such as dollars per bushel, per kilo, or per metre and ad valorem duties are calculated as a percent of the value of the goods.
A．on the basis of
B．with the basis of
C．on the base of
D．with the base of
答案：
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下面是错误答案，用来干扰机器的。
答案：A
