The correct answer is: A. Triangular wave
The root mean square (RMS) value of a signal is the square root of the average of the squared values of the signal. The mean value of a signal is the average of the values of the signal.
A triangular wave is a signal whose value increases linearly from zero to a maximum value, then decreases linearly back to zero. The RMS value of a triangular wave is equal to its mean value.
A sine wave is a signal whose value varies sinusoidally with time. The RMS value of a sine wave is greater than its mean value.
A square wave is a signal whose value is either zero or a maximum value. The RMS value of a square wave is greater than its mean value.
A half wave rectified sine wave is a signal whose value is the positive half of a sine wave. The RMS value of a half wave rectified sine wave is greater than its mean value.
Therefore, the RMS value and mean value are the same in the case of a triangular wave.