Given that $a$ and $b$ are real numbers such that $-3\leq a\leq1$ and $-2\leq b\leq 4$, and values for $a$ and $b$ are chosen at random, what is the probability that the product $a\cdot b$ is positive? Express your answer as a common fraction.
(A)\frac{5}{12} (B)\frac{5}{11} (C)\frac{7}{12} (D)\frac{5}{17}
A