1. Give CFG's for each of the following languages, and justify your answer. A. {w: w is a string of a's and b's with an even number of a's} B. {w: w is a string of a's and b's such that w is the same when written backwards, except possibly for the first and last characters} C. {a"b" : m sn} D. {a"b" : msns 2m}