(5%) Let $A$ and $B$ be two arrays and each has $n$ positive numbers. Given a permutation $\pi$ of $\{1, 2, \ldots, n\}$, we can compute the sum $\sum_{i=1}^{n} A[i] * B[\pi(i)]$. We are interested in finding the maximum of the sum, which can be maximized with a proper permutation $\pi$. Which of the following statements is/are true?