Choice A is the correct answer. The axis of symmetry for a quadratic function $y = ax^2 + bx + c$ is the vertical line given by the formula $x = -\frac{b}{2a}$.

1. Identify coefficients: $a = 1$, $b = -4$.
2. Substitute into formula: $x = -\frac{-4}{2(1)}$.
3. Simplify: $x = \frac{4}{2} = 2$.

Choice B is incorrect because of a sign error (forgot the negative in the formula). Choice C is incorrect because it forgets to divide by 2. Choice D is incorrect because of both errors.