2. Let $a$ be $150 \%$ of $b$. Then $3 b$ is $(\quad)$ of $a$.
(A) $50 \%$
(B) $66 \frac{2}{3} \%$
(C) $150 \%$
(D) $200 \%$
(E) $450 \%$
2. D.

From the problem, we know that $a=1.5 b, \frac{3 b}{a}=2=200 \%$