Explanation: After a rectifier converts AC to pulsating DC, the output still contains significant variations in amplitude, known as ripple. The filter's primary role is to smooth out these pulsations. Option A correctly states that the filter's function is "to remove the variations in amplitude of the rectifier output." This directly refers to the filter's action of attenuating the ripple component present in the pulsating DC. Option B accurately describes the desired outcome of the filtering process: "to provide a relatively unvarying DC voltage for use in the various circuits." By removing the amplitude variations (ripple), the filter ensures a stable, smooth DC voltage, which is essential for powering sensitive radio circuits without introducing hum or instability. Since both removing the ripple (A) and providing a stable DC voltage (B) are fundamental aspects of the filter's operation and purpose, C, "Either A or B," is the most comprehensive and correct answer.