单项选择题

Which of the following is mentioned as an improvement on the launch of Discovery

A．a special examination of the O ring
B．greater safety design of the crew cabin
C．redesign of the booster system
D．careful consideration of the effects of weather

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单项选择题

The word overrule in the first sentence of paragraph 2 means ______.

A．share
B．ignore
C．consider
D．know

单项选择题

It is obvious from Paragraph 4 that the chief cause leading to the disaster is ______.

A．the leakage of the O rings
B．cold weather
C．structure failures
D．the faulty fuel tank