Which expression is equivalent to $\frac{m n^2}{m n+m^2 n^2}$ ?
A$\frac{1}{n+m}$
B$\frac{n}{1+m^2 n^2}$
C$\frac{n}{1+m n}$
D$\frac{1}{m^2 n}$
A$\frac{1}{n+m}$
B$\frac{n}{1+m^2 n^2}$
C$\frac{n}{1+m n}$
D$\frac{1}{m^2 n}$