The intensity of a light pulse travelling along a communication channel decreases exponetially with distance x according to the relation `I=I_(0)e^(-ax)` where `I_(0)` is the intensity at x=0 and `alpha` is the attenuation constant. The percentage decrease in intensity after a distance of `(("In"4)/(alpha))` is
A. 0.7
B. 0.75
C. 0.8
D. 0.85
