2. (1996 National High School Competition Question) In the geometric sequence $\left\{a_{n}\right\}$, $a_{1}=1536$, common ratio $q=-\frac{1}{2}$, use $\pi_{n}$ to denote the product of its first $n$ terms, then the largest $\pi_{n}\left(n \in \mathbf{N}_{+}\right)$ is ( ).
A. $\pi_{9}$
B. $\pi_{10}$
C. $\pi_{12}$
D. $\pi_{13}$