The survey has revealed that in the past 40 years the public faith in the American government has dropped by ______.

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

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