Which is the best description of the equivalency of the two expressions? expression 1: 5x^2-2x-4+6x+3 expression 2: 6x^2-6x+6-x^2+10x-7 a: the two expressions are not equivalent because when x=2, the two expressions do not have the same value. b: the two expressions are not equivalent because when they are simplified, they do not have the same coefficients for the x^2 and x terms. c: they are equivalent because the sum of the constants is the same in both expressions d: they are equivalent because when x=2, the two expressions have the same value