In hopes of gaining some indication of the fragments' size, astronomers studied...这是目的。目的就是要求出fragment有多大。studied 后面的那一长串是得到fragment有多大的推理。通过引入另一个物质“sulfur”来判断。文章最后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.这是结论.
我认为GWD版的答案是C。第一个黑体部分,本质是evidence,只不过被astraunomer take into consideration,作为导入conclusion的argument的一部分了,所以称其为consideration并没有问题;而第二部分只是导入final conclusion的另外一个被take into consideration的部分,并不是conclusion,甚至不是interim conclusion,还是只是argument的一部分而已。