$$\left(a^{\frac{1}{z - x}}\right)^{\frac{1}{z - y}}. \left(a^{\frac{1}{x - y}}\right)^{\frac{1}{x - z}} . \left(a^{\frac{1}{y - z}}\right)^{\frac{1}{y - x}} =$$

A

a

B

0

C

xyz

D

1