Answer is energy as waves transfer energy.
hope it helps.. :)
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Mass oscillates in mechanical waves like pressure waves, or sound waves caused due to vibration.  There is no mass oscillating in an electromagnetic wave.
Amplitude is a fixed quantity for a constant wave of a frequency. The amplitude could oscillate (vary periodically) if there are multiple frequencies in a wave.
Frequency can also oscillate periodically if the wave is modulated. For example, in case of FM radio waves, the frequency oscillates in the air waves.

In a simple single frequency wave with a constant amplitude, the quantity that varies as a Sine or cosine is the energy in the wave at a point or the energy that is transmitted along the direction of propagation is an expression with Sine function in it.  The time average of energy is a constant.

So the answer is energy, which is more appropriate than other choices given.

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