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【单选题】
( )是构成市场的最基本条件,没有它就不可能有市场存在。A.
人口
B.
需求
C.
购买习惯
D.
购买力
E.
消费者收入
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【简答题】It ______ not be his car.
【单选题】f:A→B为从A到B的一个函数,下列说法正确的有
A.
函数是一个映射
B.
函数要求集合A、B是非空的数集，而映射只要求A、B是两个非空集合就可以了
C.
两种说法均正确
【单选题】It was quite a serious mistake, ____caused by carelessness.
A.
which I think was
B.
I think which was
C.
which I think it was
D.
I think which it was
【单选题】If it for his invitation the other day, I should not be here now.
A.
had not been
B.
should not be
C.
were not to be
D.
should not have been
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