The cameras of the Voyager II spacecraft detected six small, previsously unseen moons circling Uranus, (which doubles to twelve the number of staellites now known as orbiting) the distant planet.
b. doubling to twelve the number of satellites now known to orbit
d. doubling to twelve the number of satellites now known as orbiting
嘿嘿，JJ，小弟实在是不好意思的告诉你答案是B，看到你那么有信心，偶都不好意思说。该书后面的解释是“过去分词known之后为一个不定式(known to do)或一个以as引导的介词短语(as...），从而选B”。所以我说它是废话，那d为什么不可以，实在佩服你对那些短语的意思记得这么清楚。我刚预备考，T和G一起。
[补充]
be known as
以...知名; 被认为是; 称为
be known to
为...所知
be known for
因...而著名
become known
出名
make oneself known to sb.
向某人作自我介绍
make sth. known
把某事(向某人)公布
make sth. known to sb.
把某事(向某人)公布
