单项选择题

Sagittarius A is ______.

A．clearly a super-massive black hole
B．a compact cluster of normal stars
C．a single, small subject
D．still an issue of controversy
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单项选择题
Were it not for the new telescope high in the Andes Mountains, researchers would not have argued that ______.
A．Sagittarius A is a powerful emitter of radio waves
B．a super-massive black hole contains as much as a million suns
C．Sagittarius A is a super-massive black hole
D．Sagittarius A lies just at the center of the Milky Way Galaxy
单项选择题
It may be inferred from the passage that jets of gas ______.
A．around Sagittarius A were found quite unexpectedly
B．are common phenomena surrounding enormous black holes
C．only flow away from the centers of galaxies
D．are the true source of intense energy
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