一道语法题

wretdgdh

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. The some fraternal twins resembling each other greatly while others look quite dissimilar highlights an interesting and often overlooked feature of fraternal-twin pairs,namely that they vary considerably.
为什么选b？the fact of 是不是不对啊？
另外excepting放在句首也不对吧

mary1

the fact of 表达有误，通常改为：同位语从句 the fact that 从而精确表达，且look 此处不应用进行时态