The fact of some fraternal twins resembling each other greatly and others looking quite dissimilar highlights an interesting and often overlooked feature of fraternal-twin pairs, namely they vary considerably on a spectrum of genetic relatedness.

A.
The fact of some fraternal twins resembling each other greatly and others looking quite dissimilar highlights an interesting and often overlooked feature of fraternal-twin pairs, namely they vary considerably
B.
That some fraternal twins resemble each other greatly while others look quite dissimilar highlights an interesting and often overlooked feature of fraternal-twin pairs, namely that they vary considerably
C.
With some fraternal twins resembling each other greatly and others looking quite dissimilar, it highlights an interesting and often overlooked feature of fraternal-twin pairs, namely considerable variation
D.
With some fraternal twins resembling each other greatly and others looking quite dissimilar, it is a fact that highlights an interesting and often overlooked feature of fraternal-twin pairs, namely a considerable variation
E.
Because some fraternal twins resemble each other greatly and others look quite dissimilar, this fact highlights an interesting and often overlooked feature of fraternal-twin pairs, namely they vary considerably

答案Ｂ，那位可以帮忙分析讲解一下句子结构啊？　对"namely that they vary considerably" 的作用有疑问。 　

A的the fact of ... doing 结构不好, namely这个副词可以无视，A 的两个主句并列没有连接，错。
CD都用it指代了前面的句子，指代错误。
E也是两个主句连接没有连接词（this fact highlights... , namely they vary...)
排除结果选择B
B的结构也是比较好的。That引导主语从句，highlights是谓语动词，最后的namely that they vary considerably ...是宾语从句修饰feature

  Thanks!

不是很明白。
宾语从句可以修饰名词吗？