The correct answer is: A. the time required to complete one full cycle.
A waveform is a graphical representation of a function, such as a sine wave. The period of a waveform is the time required to complete one full cycle of the waveform. For example, the period of a sine wave is the time it takes for the wave to go from its maximum value to its minimum value and back to its maximum value again.
Option B is incorrect because it defines the frequency of a waveform, not the period. The frequency of a waveform is the number of cycles completed in one second.
Option C is incorrect because it defines the rise time of a waveform, not the period. The rise time of a waveform is the time required for the voltage to rise from 10% to 90% of the peak amplitude.
Option D is incorrect because it defines the amplitude of a waveform, not the period. The amplitude of a waveform is the maximum value of the wave.
Option E is incorrect because it is not a valid option.
In conclusion, the period of a waveform is the time required to complete one full cycle.