【OG13-81题求解】关于主语谓语修饰语和逗号的疑惑

Faithy

OG 13 81题：
78. Fossils of the arm of a sloth found in Puerto Rico in 1991, and dated at 34 million years old, made it the earliest known mammal of the Greater Antilles Islands.
(A) sloth found in Puerto Rico in 1991, and dated at 34 million years old, made it the earliest known
mammal of
(B) sloth, that they found in Puerto Rico in 1991, has been dated at 34 million years old, thus making it the earliest mammal known on
(C) sloth that was found in Puerto Rico in 1991, was dated at 34 million years old, making this the earliest known mammal of
(D) sloth, found in Puerto Rico in 1991, have been dated at 34 million years old, making the sloth
the earliest known mammal on
(E) sloth which, found in Puerto Rico in 1991, was dated at 34 million years old, made the sloth the earliest known mammal of

这个题是可以根据单复数排除最后选择D没错，但是我真的纠结在D选项的结构中很久了TT
想请教各位NN们确认一下，像D这样的表达方式，就主要是主语和谓语中间用逗号隔开，主语和修饰语也用逗号隔开，这样的形式在GMAT里是正确的是吗？

对于逗号的使用很是困惑！
看Jeffery2541的帖子http://forum.chasedream.com/foru ... %3D1%26typeid%3D138大概搞清楚了逗号和v-ing的用法，对其他的还是不太清楚哎。

求大牛现身解释！！！！！！！！

谢谢！！！

adamzjw

不是NN。。

Fossils of the arm of a sloth,【found in Puerto Rico in 1991】, have been dated at 34 million years old, making the sloth
the earliest known mammal on the Greater Antilles Islands.
你是指【found in Puerto Rico in 1991】？
这个成分前后被两个commas包围，作为non-essential modifier修饰主语，而且必须临近主语。因此句子就成了这样。

Faithy

adamzjw 发表于 2013-4-4 12:29
不是NN。。

Fossils of the arm of a sloth,【found in Puerto Rico in 1991】, have been dated at 34 mi ...

谢谢好同学！！！

其实我比较疑惑的主要是这个句子主语和谓语被逗号们分开了的用法，而且还是完成时，就是我不太确定这种用法，因为我之前潜意识里一直觉得这样是错的，就比如I,have been to China before.（可能类比不当啦我语法比较差~）