求助GWD一篇阅读的一道题，black hole那篇。

ewuyi

Q10 to Q12:
Astronomers theorize that a black
hole forms when a massive object
shrinks catastrophically under its own
Linegravity, leaving only a gravitational
(5)field so strong that nothing escapes it.
Astronomers must infer the existence
of black holes, which are invisible,
from their gravitational influence on
the visible bodies surrounding them.
(10)For example, observations indicate
that gas clouds in galaxy M87 are
whirling unusually fast about the galaxy’s
center. Most astronomers
believe that the large concentration
(15)of mass at the galaxy’s center is a
black hole whose gravity is causing
the gas to whirl. A few skeptics have
argued that the concentration of mass
necessary to explain the speed of the
(20)whirling gas is not necessarily a black
hole: the concentration in M87 might
be a cluster of a billion or so dim stars.

The same hypothesis might have
been applied to the galaxy NGC 4258,
(25)but the notion of such a cluster’s
existing in NGC 4258 was severely
undermined when astronomers measured
the speed of a ring of dust and
gas rotating close to the galaxy’s
(30)center. From its speed, they calculated
that the core’s density is more
than 40 times the density estimated
for any other galaxy. If the center of
NGC 4258 were a star cluster, the
(35)stars would be so closely spaced
that collisions between individual
stars would have long ago torn the
cluster apart.


Q11:
The passage asserts which of the following about the existence of black holes?
A. Astronomers first speculated about the existence of black holes when theyobserved gas whirling around the center of a particular galaxy.
B. Evidence used to argue for the existence of black holes is indirect, coming from their presumed effects on other astronomical bodies.
C. Recent observations of certain astronomical bodies have offered proof.
D. A considerable body of evidence suggests the existence of black holes, even though their behavior is not completely consistent with the laws of physics.
E. Many astronomers are skeptical about certain recent evidence that has been used to argue for the existence of black holes.

这题OA答案是B，我知道B可以从这句话看出来，Astronomers must infer the existence
of black holes, which are invisible,from their gravitational influence on the visible bodies surrounding them.但是请问A、C错在哪里啊？实在想不通。