The correct answer is C. increasing the amplitude of the wave.
In a wave, the energy is directly related to the amplitude; higher amplitude means greater energy carried by the wave. Increasing the amplitude of the wave would definitely increase its energy.
Options A, B, and D would not increase the energy of the wave. Specifically:
- A: Increasing the wavelength would generally decrease the energy for a wave of a certain type (like a sound wave).
- B: Decreasing the amplitude would decrease the energy.
- D: Decreasing the frequency does not necessarily increase energy either; in many cases, lower frequency waves carry less energy than higher frequency waves.
Therefore, the best option to increase the energy of the wave is to increase the amplitude.