Choice A is the correct answer. The discriminant formula is $\Delta = b^2 - 4ac$.

1. Identify coefficients: $a = 1$, $b = -4$, $c = 3$.
2. Substitute: $\Delta = (-4)^2 - 4(1)(3)$.
3. Calculate: $\Delta = 16 - 12 = 4$.

Choice B is incorrect because it calculates $4ac$ only. Choice C is incorrect because it subtracts in reverse ($12-16$). Choice D is incorrect because it adds ($16+12$).