单项选择题

The evidence of this passage shows that ______.

A．the presently-accepted theory of light will soon be replaced by another new theory
B．scientists do not know enough to develop the most satisfactory theory of light
C．there would be no progress in our knowledge of light unless we questioned accepted theories
D．earlier scientists always aimed at the perfectness of a theory

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单项选择题

The underlined phrase such a reaction (Para. 3) most probably refers to ______.

A．making a choice between "flight and fight"
B．reaction to cases both chemically and physically
C．responding to crises quickly
D．losing heart at the .signs of difficulties

单项选择题

Which of the following statements is TRUE

A．We can find some ways to avoid stress.
B．Stress is always harmful to people.
C．It is easy to change the habit of keeping oneself busy with work.
D．Different people can withstand different amount of stress.