At which value(s) is the expression
\[ \frac{x}{x^{2}+4} \] undefined?

A) (-2, 2)
B) x = ±2
C) never undefined
D) (-∞, -2) U (-2, 2) U (2, ∞)
E) (-∞, -2] U [-2, 2] U [2, ∞)