5. In the geometric sequence $\left.a_{n}\right\}$, the first term $a_{1}=1536$, and the common ratio $q=-\frac{1}{2}$. Let $\Pi_{n}$ represent the product of its $n$ terms, then the largest $\Pi_{n}$ is ( ).
A. $\mathrm{II}_{4}$
B. $\mathrm{H}_{11}$
C. $\mathrm{II}_{12}$
D. $\Pi_{13}$
5. C $\frac{n(n-1)}{2}$ is even, so $n \neq 11$; Furthermore, $11_{9}>0$, and $a_{10} a_{11} a_{12}=\left(\frac{1536}{1024}\right)^{3}>1$, thus $\Pi_{12}>1_{9}$; and $a_{13}=\frac{1536}{2^{12}}<1$, so $1_{13}<\mathrm{H}_{12}$, which means $\Pi_{12}$ is the largest.