The correct answer is C. 2E.
The energy of a simple pendulum is given by the equation:
$$E = \frac{1}{2}m\omega^2L^2$$
where $m$ is the mass of the pendulum, $\omega$ is the angular frequency, and $L$ is the length of the pendulum.
The angular frequency is given by the equation:
$$\omega = \sqrt{\frac{g}{L}}$$
where $g$ is the acceleration due to gravity.
When the amplitude is increased to 2A, the length of the pendulum does not change, so the angular frequency does not change. However, the energy of the pendulum is proportional to the square of the angular frequency, so the energy of the pendulum increases to 2E.
Option A is incorrect because the energy of the pendulum does not change when the amplitude is increased.
Option B is incorrect because the energy of the pendulum is proportional to the square of the angular frequency, so the energy of the pendulum increases to 2E when the amplitude is increased to 2A.
Option D is incorrect because the energy of the pendulum is proportional to the square of the angular frequency, so the energy of the pendulum increases to 4E when the amplitude is increased to 4A.