Given:
\[
x = \frac{x}{y+z} \Rightarrow y+z = 1
y = \frac{y}{z+x} \Rightarrow z+x = 1
z = \frac{z}{x+y} \Rightarrow x+y = 1
\]
Add all three:
\[
(y+z) + (z+x) + (x+y) = 3 \Rightarrow 2(x + y + z) = 3 \Rightarrow x + y + z = \frac{3}{2}
\]
Now check if all options hold — none of the algebraic identities are universally true. Test values show contradiction. Hence:
\[
\boxed{\text{None of these}}
\]