请教OG11 SC的一个问题

题目如下：
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

小弟有两点不明白。第一个是previously前的那个逗号，在什么情况下可以对多个形容词进行逗号分隔，我记得只有三个的时候才用逗号的。比如，我们是否可以说 "Jack is a tall, clever boy" 呢？

第二个是正确答案B中的"doubling"的用法，分词的逻辑主语必须是主句的主语，但这个句子的主语是"cameras"呀？

小弟有两点不明白。第一个是previously前的那个逗号，在什么情况下可以对多个形容词进行逗号分隔，我记得只有三个的时候才用逗号的。比如，我们是否可以说 "Jack is a tall, clever boy" 呢？

==》不是，两个也可以。请看OG10th SC 37：

37. While some academicians believe that business ethics should be integrated into every business course, others say that students will take ethics seriously only if it would be taught as a separately required course.

(A)
                        only if it would be taught as a separately required course

(B)
                            only if it is taught as a separate, required course   ==》两个形容词并列用逗号分开的

(C)
                        if it is taught only as a course required separately

(D)
                        if it was taught only as a separate and required course

(E)
                        if it would only be taught as a required course, separately

第二个是正确答案B中的"doubling"的用法，分词的逻辑主语必须是主句的主语，但这个句子的主语是"cameras"呀？

==》句末现在分词做状语，可以做结果或者伴随发生。逻辑主语不一定需要时主语主语。

OG 259：

259. Five fledgling sea eagles left their nests in western Scotland this summer, bringing to 34 the number of wild birds successfully raised since transplants from Norway began in 1975.

(A)   bringing

(B)    and brings

(C)    and it brings

(D)   and it brought

(E)    and brought

非常感谢crowkiller兄