关于非限定性定语从句一问

BY GMAT 语法全解 Ch8-22：

The cameras of the Voyager II spacecraft detected six small, previously unseen moons circling Uranus, which doubles to the twelve the number of satellites now known as orbiting the distant planet.

A  which doubles to the twelve the number of satellites now known as orbiting

B  doubling to the twelve the number of satellites now known to orbit

C  which doubles to twelve the number of satellites now known in orbit around

D  doubleing to twelve the number of satellites now known as orbiting

E  which doubles to twelve the number of satellites now known that orbit

答案为B。解释说ACE中which定语从句修饰Uranus，逻辑意思不合理，而且在标准书面语中，which也不能理解为指代前面的整个句子。而B，-ing分词短语在句尾做伴随结果状语。我有点不理解，非限定性定于从句从来都被教说可以修饰句子的，B中的现在分词的逻辑主语又是谁呢，不也该是就近的Uranus吗？想不明白B、E到底该如何分辨，请高人指点！Thanks.

清楚考点很重要。

考点：GMAT规定的标准英语书面语法中，it/which/this 都不可能指整个句子；宾语后置： doubling to twelve the number of satellites: doubling the number of satellites to twelve; Be known for sth,/ as sb./ to sb./ to do sth. ;      Be konwn that 不存在。

谢谢指点。

此外，在哪里能看到GMAT的特殊语法约定呢？