GWD-9-Q3:
Because of wireless service costs plummeting in the last year, and as mobile phones are increasingly common, many people now using their mobile phones to make calls across a wide region at night and on weekends, when numerous wireless companies provide unlimited airtime for a relatively small monthly fee.
A.Because of wireless service costs plummeting in the last year, and as mobile phones are increasingly common, many people（第一because of 短语和as从句不能并列平行,第二，后文中有using表明用现在进行时）
B.As the cost of wireless service plummeted in the last year and as mobile phones became increasingly common, many people（第一用became无法表示现在的动作，第二没有用现在进行时）
C.In the last year, with the cost of wireless service plummeting, and mobile phones have become increasingly common, there are many people（and…没有并列的对象）
D.With the cost of wireless service plummeting in the last year and mobile phones becoming increasingly common, many people are
E.While the cost of wireless service has plummeted in the last year and mobile phones are increasingly common, many people are（时态问题？）
答案是D，我选的是E，不明白为什么. 是因为时态错了吗？？
有没有NN顺便能够指点一下WITH的用法啊~ | 
