Astronomer: Observations of the Shoemaker-Levi comet on its collision course with Jupiter showed that the comet broke into fragments before entering Jupiter's atmosphere in 1994, but they did not show how big those fragments were. In hopes of gaining some indication of the fragments' size, astronomers studied spectrographic analyses of Jupiter's outer atmosphere. These analyses revealed unprecedented traces of sulfur after the fragments' entry. The fragments themselves almost certainly contained no sulfur, but many astronomers believe that the cloud layer below Jupiter's outer atmosphere does contain sulfur. Since sulfur would have seeped into the outer atmosphere if comet fragments had penetrated this cloud layer, it is likely that some of the fragments were at least large enough to have passed through Jupiter's outer atmosphere without being burned up.
In the astronomer's argument, the two portions in boldface play which of the following roles?
A. The first presents a circumstance for which the astronomer offers an explanation; the second is part of that explanation.
B. The first acknowledges a consideration that weighs against the conclusion of the argument; the second is that conclusion.
C. The first acknowledges a consideration that weighs against the conclusion of the argument; the second provides evidence in support of that conclusion.
D. The first provides evidence in support of the conclusion of the argument; the second acknowledges a consideration that weighs against that conclusion.
E. The first is a judgment advanced in support of the conclusion of the argument; the second is that conclusion.

I had a hard time to detect conclusion and that led me to answer it wrongly!
What is the conclusion?