A student appears for tests I, II and III. The student is successful if the passes either in tests I and II or tests I and III. The probabilities of the student passing in tests I, II and III are p,q and `(1)/(2)`, respectively. If the probability that the student is successful, is `(1)/(2)`, then
A. p=q=1
B. `p=q=(1)/(2)`
C. p=1,q=0
D. `p=1,q=(1)/(2)`
Select the correct answer from above options