B. Use three types of regular polygon tiles with equal side lengths to pave the ground, with their vertices fitting together perfectly, leaving no gaps. If the number of sides of these three regular polygons are $x$, $y$, and $z$, then the value of $\frac{1}{x}+\frac{1}{y}+\frac{1}{z}$ is $(\quad)$.
(A) $\frac{1}{3}$
(B) $\frac{1}{2}$
(C) $\frac{2}{3}$
(D) 1
B. B.

The interior angles of these three regular polygons are respectively equal to
$$
\frac{x-2}{x} \times 180^{\circ}, \frac{y-2}{y} \times 180^{\circ}, \frac{z-2}{z} \times 180^{\circ} \text{. }
$$

Since the three tiles fit together perfectly without gaps, the sum of these three angles is $360^{\circ}$.
$$
\begin{array}{l}
\text { Therefore, } \frac{x-2}{x}+\frac{y-2}{y}+\frac{z-2}{z}=2 \\
\Rightarrow \frac{1}{x}+\frac{1}{y}+\frac{1}{z}=\frac{1}{2} .
\end{array}
$$