单项选择题

What can we learn from the passage

A．It is very expensive to build a wind tunnel．
B．Wind tunnels are very essential in testing planes．
C．Scientists still have a lot to learn about wind tunnels．
D．There are new ways to feed air to the test section．

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热门试题

单项选择题

As mentioned in the last paragraph，a wind tunnel can be used to find out____.

A．how fast a plane can rise
B．how smooth a plane’s surface is
C．how a plane lands in a strong wind
D．how a plane drops at a low height

单项选择题

The underlined words“this fact”in Paragraph 3 refer to the fact that____．

A．it costs a lot to test a plane
B．the wings are not good enough
C．some problems are found with a plane
D．the wings meet the high-speed air flow in the tunnel