The greatest road system built in the America prior to the arrival of Christopher Columbus was the Incan highway,which,over 2,500 miles long and extending from northern Ecuador through Peru to Southern Chile.

B Columbus was the Incan highway,over 2,500 miles in length,and etended

E Columbus,the Incan highway was over 2,500 miles long,extending

B有什么错啊，不能用in length?

E不是重心转移了吗

extend逻辑上应该是修饰the Incan highway， 但B中extended语法上却和was平行，主语为The greatest road system，逻辑上不通。

相比之下，E中前句做主语同位语，后面extending修饰主语，简单明了。

The problem of B is the verb "extend" was used to reflect the road system.

It should be reflecting the Incar highway.

The "incar highway" is a tong wei yu, better choice.

 关键在于extend的动作发起者是the Incan highway

我的理解是这样的

B的关键不是extend的发出者是谁，既然A=B, 你可以说B extend 当然也可以说A

extend啦！关键是句子结构不合理:and extend 是和什么平行的呢，如果说是个was

the Incan Highway平行，显然很别扭，我们通常不会在两个并列句子谓语一个是be

动词，一个是实义动词的情况下并列并省略主语的，实在不行第二个主语还是会用

代词补出来。常见的情况是都是be 动词或都是实义动词。

可能需要借助一些语感。