求助一道magoosh单空题

vicipeteUID: 3363516

Collaboration between students, while promising—students who work together rarely are in the bottom half of the class—does not tend to account for the success of students at the very top of the class, students who work  autonomously/independently.

这个句子的结构没看懂，求助。。。。
while promising是什么意思？两个破折号之间插入语中的students指代不是students at the very top of the class？？？那和in the bottom half of the class不是矛盾了嘛。。。
请各位大神帮帮忙。。。。不胜感激

muybienwUID: 3532583

while promising说的是collaboration between students，破折号里的内容是描述怎么promising的。
后面does not...的主语是collaboration between students。
最后的students who...是前面students at the very top of the class的同位语。

所以句子的大意是：
collaboration虽然promising（因为collaborate的学生很少垫底），但是无法解释top学生（那些work automously/independently的学生）的成功

天薇凉UID: 3403940

破折号之间的内容单独看就行了~

vicipeteUID: 3363516

muybienw 发表于 2014-8-1 13:53
while promising说的是collaboration between students，破折号里的内容是描述怎么promising的。
后面does ...

thx
我以为rarely修饰work。。。。。。。