49. The cameras of the Voyager II spacecraft detected six small, previously unseen moons circling Uranus, which doubles to twelve the number of satellites now known as orbiting the distant planet
A. which doubles to twelve the number of satellites now known as orbiting
B. doubling to twelve the number of satellites now known to orbit
C. which doubles to twelve the number of satellites now known in orbit around
D. doubling to twelve the number of satellites now known as orbiting
E. which doubles to twelve the number of satellites now known that orbit
 
1．非限制性定语从句（一级排除A,C,E）

非限制性定语从句 which 指向前面的名词(这里是不是指前面的这件事所以不能用which?)

现在分词在句末表示伴随

2．词法 ：A as B，Ａ/B 对应。 Known to orbit 比 known as orbiting … 好。