og12~41页40题，请教请教

viviangao1110

40. In 1995 Richard Stallman, a well-known critic of the patent system, testified in Patent Office hearings that, to test the system, a colleague of his had managed to win a patent for one of Kirchhoff’s laws, an observation about electric current first made in 1845 and now included in virtually every textbook of elementary physics.

(A) laws, an observation about electric current first made in 1845 and
(B) laws, which was an observation about electric current first made in 1845 and it is
(C) laws, namely, it was an observation about electric current first made in 1845 and
(D) laws, an observation about electric current first made in 1845, it is
(E) laws that was an observation about electric current, first made in 1845, and is

BDE都可以排除，C中namely，it was an是wordy
有一点不明白的，前文说了是one of k's laws，后面A中说的an observation是不是指的前面的one？
那为什么说c中的it无法指代呢？it不正好指代前面的one么？
请教指导~~~~

carolballack

Richard Stallman...testified...that...laws（已构成独立句子），后面是修饰成分。it作为主语引入新句。两个独立句子不能用逗号隔开。