Simplify: 3a2b39ab2\frac{3a^2b^3}{9ab^2}9ab23a2b3 for a,b≠0a, b \neq 0a,b=0.
ab3\frac{ab}{3}3ab
ababab
ab23\frac{ab^2}{3}3ab2
a3b\frac{a}{3b}3ba