X1 and X2 represent number of occurrences of event A and 8 that follow Poisson distribution with mean rate λ1 and λ2 , If Y1 and Y2 are inter-occurrence times of event A and B, then min(Y1, Y2 ) follows 1.       Exponential distribution with mean rate min (λ1, λ2 ) 2.       Exponential distribution with mean rate (λ1 + λ2 ) 3.       Poisson distribution with mean rate (λ1 - λ2 ) 4.       Poisson distribution with mean rate (λ1 + λ2 )