求助，GWD-18-Q41，with的问题

kiki_11

At the turn of the twentieth century, forest covering as much as 90 percent of Thailand and accommodating as many as 300,000 elephants, a third of them domesticated and performing various essential tasks.

A.    covering as much as 90 percent of Thailand and accommodating as many as 300,000 elephants, a third of them

B.    covering as much as 90 percent of Thailand accommodated as much as 300,000 elephants, and a third of them were

C.    covered as much as 90 percent of Thailand and accommodated as much as 300,000 elephants, with a third

D.    covered as much as 90 percent of Thailand and accommodated as many as 300,000 elephants, a third of them

      E.  covered as much as 90 percent of Thailand and accommodating as many as 300,000 elephants, with a third of them

我选的是E,答案说with修饰的是主语forest，为什么不能修饰elephants呢？还有D，a third of them...是一个同位语吗？可是a third of them...这部分看起来很像一个独立的句子，缺少and，所以我把D排除了。a third of them...是什么用法呃？