2. The unit prices of three types of books are 10 yuan, 15 yuan, and 20 yuan, respectively. A school plans to spend exactly 500 yuan to buy 30 books of the above types. Then the number of different purchasing plans is ( ).
(A) 9
(B) 10
(C) 11
(D) 12
2. C.

Let the quantities of the three types of books purchased be $a$, $b$, and $c$.
$$
\begin{array}{l}
\text { Then }\left\{\begin{array}{l}
a+b+c=30, \\
10 a+15 b+20 c=500
\end{array}\right. \\
\Rightarrow\left\{\begin{array}{l}
b=20-2 a, \\
c=10+a .
\end{array}\right.
\end{array}
$$

Thus, $a$ has 11 possible values (0, $1, \cdots, 10$). For each value of $a$, the corresponding $b$ and $c$ can be uniquely determined. Therefore, there are 11 different purchasing plans.