option (c) is incorrect
option(A) -we know that in case of stop and wait ,efficiency =1/(1+2a) where a=PT/TT =>a=(d/v)*(B/L) where d is distance, v is propagation speed ,B is bandwidth and L is data length
here on putting values ,efficiency= 1/(1+2*d/v*B/L) ,we can say clearly when L increases efficiency also increases hence option A is correct.
option (B)-same as option A so true
option (C)-from the expression we can say directly that efficiency and distance is inversely proportional =>c is incorrect
option (D)-capacity of channel in case of stop and wait=B*PT so from the expression we can say if capacity increases then efficiency decreases. =>option D is correct