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

According to the passage, which of the following is TRUE

A．Energy only emits from Sagittarius A.
B．There are many strong energy sources.
C．Energy comes from a black hole.
D．Energy emits from any regions surrounding Sagittarius A.

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