Give the context-free grammars that generate three of the following languages. a. A_1 {a^n b^m c^k |n + K = m where n, m, k > 0) b. A_2 = {a^2n b^m c^2m d^n|n, m > 0}. A_3 (w | the length of w is even and starts & ends with the same symbol) d. A (w | w is a palindrome, and has an even length)