2. If $x+y+z \neq 0, a=\frac{x}{y+z}, b=\frac{y}{x+z}$, $c=\frac{z}{x+y}$, then $\frac{a}{a+1}+\frac{b}{b+1}+\frac{c}{c+1}=(\quad)$.
(A) 0
(B) 1
(C) $a+b+c$
(D) Uncertain
2. (B).
$$
\frac{a}{a+1}=\frac{\frac{x}{y+z}}{\frac{x+y+z}{y+z}}=\frac{x}{x+y+z} \text {. }
$$

Therefore,
$$
\frac{b}{b+1}=\frac{y}{x+y+z}, \frac{c}{c+1}=\frac{z}{x+y+z} .
$$
$\therefore$ Adding them together gives the result. Hence, the answer is (B).