请问这道题怎么解？

confuser2008

14. GWD17-Q14:

Whereas lines of competition are clearly defined in the more established industries, in the Internet industry they are blurred and indistinct, as companies that compete one day may be partners the next.

 

A.    Whereas lines of competition are clearly defined in the more established industries, in the Internet industry they are blurred and indistinct, as companies that compete

B.    Although the lines of competition are clearly defined in industries that are more established, they are blurred and indistinct in the Internet industry, as competing companies

C.    The lines of competition are clearly defined in the more established industries, unlike the Internet where they are blurred and indistinct, as companies that compete

D.    Unlike more established industries, where the lines of competition are clearly defined, they are burred and indistinct in the Internet industry, as companies that compete

E.     Unlike more established industries, with clearly defined lines of competition, those of the Internet industry are blurred and indistinct, as competing companies

为什么答案是 B 而不是 A？

谢谢

另外什么地方能找到关于 GWD verbal 部分的解题解释呀？

我在飞

A的主句部分THEY 指代不清,有可能指代LINES 或INDUSTRIES,

B中的指代很清晰