GWD19-3 请指教

Q3（问问问）:

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.

1. Because of wireless service costs plummeting in the last year, and as mobile phones are increasingly common, many people

2. As the cost of wireless service plummeted in the last year and as mobile phones became increasingly common, many people

3. In the last year, with the cost of wireless service plummeting, and mobile phones have become increasingly common, there are many people

4. With the cost of wireless service plummeting in the last year and mobile phones becoming increasingly common, many people are(with独立主格结构)

5. While the cost of wireless service has plummeted in the last year and mobile phones are increasingly common, many people are(为啥错了，难道是while的原因)

同學

我個人覺得因為while沒有"因為"的意思所以改變了原始的句意

且has plummeted用last year似乎不妥