A student appears for tests 1, 2 and 3. The studentis successful if he passes either in tests 1 and 2 or tests 1 and 3. The probabilities of the student passing in tests 1, 2 and 3 are p, q and `(1)/(2)`, respectively. If the probability that the student is successful is `(1)/(2)`, then
A. `p=1, q=0`
B. `p=(2)/(3), q=(1)/(2)`
C. `p=(3)/(5), q=(2)/(3)`
D. infinitely values of p and q
