Explanation: Zero beat is a fundamental concept in radio frequency measurement, relying on the principle of heterodyning. When two radio frequencies are mixed together, they produce sum and difference frequencies. The "beat frequency" is the difference between the two input frequencies. As one frequency is adjusted to become closer to the other, this beat frequency becomes lower in pitch. When the two frequencies are exactly identical, their difference is zero. At this point, the beat tone disappears entirely, indicating that the two signals are precisely on the same frequency. This precise matching is called "zero beat" and is a very accurate method for tuning or measuring frequencies. Option B is incorrect because the frequencies are being compared, not suppressed. Option C is also incorrect; "nulling" a transmitter refers to minimizing its output, which is unrelated to the process of frequency comparison via zero beat.