请教一道NO9的阅读

jessietinUID: 2125219

Until recently astronomers have been puzzled by the

fate of red giant and supergiant stars. When the core

of a giant star whose mass surpasses 1.4 times the pre-

sent mass of our Sun (M⊙) exhausts its nuclear fuel, it

(5)is unable to support its own weight and collapses into

a tiny neutron star. The gravitational energy released

during this implosion of the core blows off the remain-

der of the star in a gigantic explosion, or a supernova.

Since around 50 percent of all stars are believed to
(10)begin their lives with masses greater than 1.4M⊙,

we might expect that one out of every two stars would

die as a supernova. But in fact, only one star in thirty

dies such a violent death. The rest expire much more

peacefully as planetary nebulas. Apparently most
(15)massive stars manage to lose sufficient material that

their masses drop below the critical value of 1.4 M⊙

before they exhaust their nuclear fuel.

Evidence supporting this view comes from observa-

tions of IRC+10216, a pulsating giant star located
(20)700 light-years away from Earth. A huge rate of mass

loss (1 M⊙ every 10,000 years) has been deduced from

infrared observations of ammonia (NH3) molecules

located in the circumstellar cloud around IRC+10216.

Recent microwave observations of carbon monoxide
(25)(CO) molecules indicate a similar rate of mass loss and

demonstrate that the escaping material extends out-

ward from the star for a distance of at least one light-

year. Because we know the size of the cloud around

IRC+10216 and can use our observations of either
(30)NH3 or CO to measure the outflow velocity, we

can calculate an age for the circumstellar cloud.

IRC+10216 has apparently expelled, in the form

of molecules and dust grains, a mass equal to that of

our entire Sun within the past ten thousand years. This
(35)implies that some stars can shed huge amounts of matter

very quickly and thus may never expire as supernovas.

Theoretical models as well as statistics on supernovas

and planetary nebulas suggest that stars that begin

their lives with masses around 6 M⊙ shed sufficient
(40)material to drop below the critical value of 1.4M⊙.

IRC+10216, for example, should do this in a mere

50,000 years from its birth, only an instant in the life

of a star.

But what place does IRC+10216 have in stellar evo-
(45)lution? Astronomers suggest that stars like IRC+10216

are actually “protoplanetary nebulas” –old giant stars

whose dense cores have almost but not quite rid them-

selves of the fluffy envelopes of gas around them. Once

the star has lost the entire envelope, its exposed core be-
(50)comes the central star of the planetary nebula and heats

and ionizes the last vestiges of the envelope as it flows

away into space. This configuration is a full-fledged

planetary nebula, long familiar to optical astronomers.


23. The view to which line 18 refers serves to


(A) reconcile seemingly contradictory facts

(B) undermine a previously held theory

(C) take into account data previously held to be

insignificant

(D) resolve a controversy

(E) question new methods of gathering data

请问为什么选A啊？

苏梳眠UID: 2717864

此题不在18行，而在于18行的前一句。
Apparently most ，massive stars manage to lose sufficient material that their masses drop below the critical value of 1.4 M⊙ before they exhaust their nuclear fuel.
这一句是为了上述与theory相矛盾的现象给出了解释，而后面的evidence则是其support的作用。
从第一句可见，全篇文章类型是解释现象型~

jessietinUID: 2125219

谢谢~~ 2# 苏梳眠