A magnetic flux through a stationary loop with a resistance `R` varies during the time interval `tau` as `phi=at(tau-t)`. Find the amount of the generated in the loop during that time
A. `(atau^2)/(2R)`
B. `(a^2tau^2)/(3R)`
C. `(2a^2tau^3)/(3R)`
D. `(atau)/(3R)`