In 1970 Professor Fellswoop Earned $12,000;in 1980 He Earned $24,000;and

In 1970 Professor Fellswoop earned $12,000;in 1980 he earned $24,000;and in 1990 he earned $36,000.If the CPI was 40 in 1970,60 in 1980,and 100 in 1990,then in real terms,Professor Fellswoop's salary was highest in

A) 1970, and lowest in 1980.
B) 1990, and lowest in 1980.
C) 1980, and lowest in 1970.
D) 1990, and lowest in 1970.