prep旧 关于RUN-ON句子的错误，求教

chaomat1988

Sixty-five million years ago, accordingto some scientists, an asteroid bigger than Mount Everest

slammed into North America, which,causing plant and animal extinctions, marks the end of the

geologic era known as the CretaceousPeriod.

(A) which, causing plant and animalextinctions, marks

(B) which caused the plant and animalextinctions marking

(C) and causing plant and animalextinctions that mark

(D) an event that caused plant and animalextinctions, and it marks

(E) an event that caused the plant andanimal extinctions that mark

答案是E，我选了D， 注解说IT指代不清 就近指代AN EVENT不对吗  然后  ,AND IT MARKS 什么叫 RUN-ON啊，，， ,AND IT 这里为什么不行呀  求教 感恩！！！！！

hebelong

run-on 就是一个句子里面不止一个 “主语+谓语”的形式，it 前面不止event是单数吧，plant也是啊

chaomat1988

,and不是表示另外起一个句子了吗  可以换主语的呀，，，，脑子昏啊 求教

sarax

and后面的句子主句是代词的话最好和and前句子的主语对应，也就是it指的应该是asteroid