For a simple harmonic motion energy is given with:

Where k is a constant that depends on the type of the wave you are looking at and A is amplitude.
Let's calculate the energy of the wave using two different amplitudes given in the problem:

We can see that energy associated with the wave is 4 times smaller when we decrease its amplitude by half. So the answer should be C.
Answer: amplitude
Explanation: This describes the maximum amount of the displacement of a particle from it rest position. Usually, it is measured in metres
Since we are considering AM which is amplitude modulation, a technique used in electronic communication, most commonly for broadcasting information through a radio carrier wave. In amplitude modulation, the amplitude (signal strength) of the carrier wave is diversified in proportion to that of the message signal being broadcasted.
Answer: A capacitor.
Explanation:
The capacitor is a passive element that is used in electronics to store electrical energy maintaining an electrical field. The simpler case of a capacitor is the parallel plates capacitor.
It consists of two parallel metal plates separated by a distance D, in this case, the air between the plates works as a dielectric, as the plates do not touch each other and are separated by a dielectric, the charge is stored in the surface plates.
There are a lot of other types of capacitors, the most used in actuality may be the cylindrical one, where instead of parallel plates, it uses two concentric cylinders, and the space between the cylinders is filled with a dielectric/insulator.
A bridge supported by vertical cables which then leads to more support from larger cables.