有个GWD里的问题请教下哈

Arctic terns, being true long-distance migrants, they nest in coastal wetlands of northern Europe but fly south for thousands of miles to spend the European winters in Antarctica. 

A. Arctic terns , being true long distance migrants, they nest in coastal wetlands of northern Europe
B. Arctic terns are true long distance migrants, nesting in coastal wetlands of northern Europe
C. Being that they are true long distance migrants, arctic terns nest in coastal wetlands of northern Europe
D. Nesting in coastal wetlands of northern Europe, arctic terns are true long distant migrants
E. True long distance migrants, arctic terns nest in coastal wetlands of northern Europe

我选的E，答案选C

为什么呢？

E如果把逗号去掉，或者在arctic terns后面再加一个逗号就可以成为正确选项了。

这道题主要是考nest和未划线部分fly的平行。

不同意...E前面是个同位语成分，不可以去掉逗号

另外，怎么能在主语位于谓语加逗号呢？