$$X = \frac{a - b}{a + b}, Y = \frac{b - c}{b + c}, Z = \frac{c - a}{c + a} \Rightarrow \frac{1 + x}{1 - x}.\frac{1 + y}{1 - y}.\frac{1 + z}{1 - z} =$$

A

0

B

$$a + b + c$$

C

$$ab + bc + ca$$

D

1