For a given reaction of first order, it takes `20` minutes for the concentration to drop from `1.0 "mol liter"^(-1)` to `0.6 "mol litre"^(-1)`. The time required for the concentration to drop from `0.6 "mol litre"^(-1)` to `0.36 "mol litre"^(-1)` will be
A. more than 20 minutes
B. less than 20 minutes
C. equal to 2 minutes
D. inifinity