Let p be the probability of happening of an event , and q of its non- happening then the total chance of r successes in n trials ` 0 le r le n , ` is
A. `""^(n )C_(r) .p^(r) . Q^(n-r)`
B. `""^(n)C_(r).p^(r-1).q^(r+1)`
C. `""^(n)C_(r).P^(r+1).q^(r-1)`
D. `""^(n)C_(r).P^(r ).q^(r )`
