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

请教B项的结构，highlights．．．and．．overlooked，为什么时态不一致．还有，namely that they vary considerably什么意思，充当什么成分？

thanks

解答一下：

That some fraternal twins resemble each other greatly while others look quite dissimilar 主语，因为是个长句，所以必须前面加THAT的highlights （谓语动词）

an interesting and often overlooked （这个OVERLOOKED是过去分词作为修饰后面feature的，和interesting 平行的)feature of fraternal-twin pairs,

namely that they vary considerably（补充状语从句，对前面整个句子进行补充） ........