Find all vertical asymptotes, x = a, of the following function. For each value of a, evaluate lim f(x), lim f(x), and lim f(x). Use co or - co when appropriate. x-at x-a- x-a x2 - 10x + 21 f(x) = x2 - 5x + 6 . . . . . Select the correct choice below, and fill in the answer box if necessary. O A. The vertical asymptote is x = The limits at this vertical asymptote are lim f(x) = lim f(x) = and lim f(x) = X-a X-a x->a O B. The vertical asymptote is x = 7 . The limits at this vertical asymptote are lim f(x) = lim f ( x ) = and lim f(x) does not exist and is neither co nor - co. x-at x->a X-a O C. There is no vertical asymptote