求问PREP-31中AS的 用法

31. A recent review of pay scales indicates that CEO’s now earn an average of 419 times more pay than blue-collar workers, compared to a ratio of 42 times in 1980.

1. that CEO’s now earn an average of 419 times more pay than blue-collar workers, compared to a ratio of 42 times

2. that, on average, CEO’s now earn 419 times the pay of blue-collar workers, a ratio that compares to 42 times

3. that, on average, CEO’s now earn 419 times the pay of blue-collar workers, as compared to 42 times their pay, the ratio

4. CEO’s who now earn on average 419 times more pay than blue-collar workers, as compared to 42 times their pay, the ratio

5. CEO’s now earning an average of 419 times the pay of blue-collar workers, compared to the ratio of 42 times

答案：C

请大牛们给讲解一下as compared to的用法，用在这里觉得有点突兀，是否为壮语从句的省略形式，如果是，省略的主语应该是什么呢？

多谢！

省略了"CEO的工资"和"蓝领的工资"