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【单选题】
假设有个实体集名叫购买情况(顾客号,产品号,购买时间,购买数量),若一个顾客同一时间可以购买多种商品,但一个顾客在不同时间对同一个产品购买多次,但同一顾客同一时间对同一产品只能购买一次,则此实体集的码是 _______。 A . B. C. D.A.
顾客号
B.
产品号
C.
（顾客号，产品号）
D.
（顾客号、产品号、购买时间）
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举一反三
【单选题】It is reported _____ great changes have been made with the application of the new policy.
A.
which
B.
that
C.
while
D.
what
【简答题】Some people prefer the old system, so they might resist the new policy. Some people might resist the new policy because of their ____________ the old system.
【单选题】The Prime Minister explained the new policy of his government in great detail so as to win the support of his people.
A.
at last
B.
at length
C.
at most
D.
at least
【单选题】What will happen in January?
A.
A new work time will be issued.
B.
The new policy will go into effect.
C.
The current health care plan will expire.
D.
The personnel department will address any problems.
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