Determine the vertical asymptote(s) of the function. If none exists, state that fact.
$f(x) = \frac{x+3}{x^3 - 10x^2 + 21x}$
Select the correct choice below and, if necessary, fill in the answer box(es) to complete your choice.
A. The function has three vertical asymptotes. The leftmost asymptote is , the middle asymptote is and the rightmost asymptote is . (Type equations.)
B. The function has two vertical asymptotes. The leftmost asymptote is and the rightmost asymptote is . (Type equations.)
C. The function has one vertical asymptote, . (Type an equation.)
D. The function has no vertical asymptotes.