The correct answer is option 'C': all the harmonics should be present.

Explanation:

A signal is said to be distorted when its waveform is altered or modified in some way compared to the original waveform. Distortion can be caused by various factors such as non-linearities in the system, interference, noise, or improper amplification.

In the context of signals, harmonics refer to the multiples of the fundamental frequency. The fundamental frequency is the lowest frequency component of a signal, while harmonics are higher frequencies that are integer multiples of the fundamental frequency.

When a signal is reproduced without distortion, it means that the reproduced signal is an exact replica of the original signal. In order to achieve this, all the harmonics of the signal should be present in the reproduction.

Here is a more detailed explanation of each option:

a) Only the fundamental is required: If only the fundamental frequency is reproduced, the resulting signal would be a sine wave with the same frequency as the original signal. However, this would not capture the complete waveform and characteristics of the original signal, leading to distortion.

b) Only the fundamental and first harmonic is required: Adding the first harmonic (twice the frequency of the fundamental) to the fundamental frequency would result in a square wave. While this captures some additional characteristics of the original signal, it still does not fully represent the complete waveform and all the harmonics of the original signal.

c) All the harmonics should be present: In order to reproduce a signal without distortion, all the harmonics of the original signal should be present in the reproduction. This means that the reproduction should accurately capture the entire frequency spectrum of the original signal, including all its harmonic components.

d) None of these: Since option 'c' is the correct answer, option 'd' can be eliminated.

In summary, to reproduce a signal without distortion, it is necessary to include all the harmonics of the original signal in the reproduction. This ensures that the complete waveform and characteristics of the original signal are accurately captured.