单项选择题

Which of the following, if true, would most seriously undermine the validity of the model of star formation that is presented in the passage

A．A star is discovered that emits lower levels of trace ions than those discovered by x-rays of our galaxy's sun.
B．A section of the universe is discovered to lack both stars and any sort of interstellar medium.
C．A galaxy is discovered with a negative rate of star formation.
D．In one corner of the galaxy, coronal gas is discovered to rarify as it becomes cooler.
E． A superbubble is found of equal mass to the galaxy surrounding it.

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单项选择题

According to the passage, the more superbubbles that exist in a galaxy,

A．the longer the star-formation process will take place
B．the greater the amount of interstellar gas in the galaxy
C．the higher the positive feedback rate of star formation in the galaxy
D．the less magnetic activity in that galaxy
E． the more regular the intervals of star formation

单项选择题

According to the passage, which of the following is true about the way stars usually form

A．They tend to overlap as they appear.
B．They tend to result from the residual matter of supernovas.
C．They tend to generate in sudden irregular fits.
D．They tend to destroy their progenitor clouds.
E． They tend to form away from gas coronas.