[if gte mso 9]> BOSTON (AP) - The average cost of a gallon of gas in Massachusetts has fallen three cents in the past week. AAA Southern New England reports Monday that self-serve, regular has dropped to an average of $3.56 per gallon, three cents below the national average. The current in-state price is 31 cents lower than at the same time last year and 13 cents lower than a month ago. AAA found self-serve, regular selling as low as $3.32 per gallon and as high as $3.75. Cox Media Group