7. As shown in the figure, the volume of the right triangular prism $A B C-A_{1} B_{1} C_{1}$ is $V$, and points $P$ and $Q$ are on the side edges $A A_{1}$ and $O C_{1}$, respectively, such that $A P=C_{1} Q$. Then the volume of the quadrilateral pyramid $B-A P Q C$ is ( ).
A. $\frac{V}{2}$
B. $\frac{V}{3}$
C. $\frac{V}{4}$
D. $\frac{V}{6}$
7. B. Connect $A_{1} B, B_{1} C$, we know $V_{B-A_{1} A C C_{1}}=\frac{2}{3}$, and $V_{B-A P C Q}=\frac{1}{2} V_{B-A_{1} A C C_{1}}$.