单项选择题

With what topic is the passage mainly concerned()

A. Mechanisms for safer navigation.
B. The economic structure of the marketplace.
C. A specific group of commodities.
D. The advantages of lowering taxes.

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单项选择题

22()

A.did
B.hoped
C.studied
D.thought

单项选择题

不同的一项是（）

A.whistle
B.which
C.wheat
D.whole