If two perfect sine waves have the same frequency and the same phase, the composite wave

• A. Is a sine wave with an amplitude equal to the difference between the amplitude of the waves
• B. Is a sine wave with an amplitude equal to the sum of the amplitudes of the two original waves
• C. Is not a sine wave, but has the same frequency as the two input waves
• D. Has zero amplitude (ie, it does not exist) because the two input waves cancel each other out.