求助prep2中的137题，急！

Blaming its recent troubles on a widening recession and slow rate of technology spending, the computer company announced that it would cut 10 percent of its workforce--more than 2,000 jobs--and expected to report a loss in its third quarter.

(A) company announced that it would cut 10 percent of its workforce--more than 2,000 jobs--and expected to report a

(B) company announced that there would be a cut--10 percent of its workforce, which was more than 2,000 jobs--and expected a reported

(C) company announced the cutting of its workforce by 10 percent, more than 2,000 jobs, and it expected a reported

(D) company's announcement included the cutting of its workforce by 10 percent, or more than 2,000 jobs, and expecting to report a

(E) company's announcement included cutting its workforce--which is more than 2,000 jobs--and expecting there to be a reported

答案是a

prep语法笔记上说c是run-on错误，可是第二个分句前面有一个“, and”连接阿，为什么还是run-on错误呢？

我碰到很多这样的题了，不明白为什么。