GWD 14-7

Q7:

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

请教答案B中，a ratio that compares to 42 times in 1980， a ratio是谁的同位语？怎么解释这句话？