求教 GWD5-31

Q31:

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                       
   

namely that/to 用法比较固定了....

表示对前文的进一步解释....其后一般问一句话的重点内容.

Since 1990,UK researchers could create and use embryos for limited research purposes,namely to treat infertility and detect birth defects.