gwd-6-19

cournot

   Q19: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.

1. 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
2. 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

3. 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
4. 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
5. 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  

the answer is B,what's wrong with E?

slickwx

我的感觉是BECAUSE 从句和后面那句没有因果关系,还有NAMELY后面的THAT应该是不能少的.

cournot

谢谢楼上，namely是副词，不能做连词，E中fact highlights an interesting and often overlooked feature of fraternal-twin pairs, namely they vary considerably   2个句子就没有连词了。

territory157

namely that是同位语的用法，是对前面主句的补充说明。