Option A: Incorrect. Two tones of the same frequency shifted 90 degrees aren't used - that's a single tone with phase shift, not a two-tone test. Two-tone tests need two different frequencies. Option C: Incorrect. Two swept frequency tones aren't used - two-tone tests use fixed frequencies, not swept. Swept tones are for different tests. Option D: Incorrect. Square wave signals aren't used - two-tone tests use sine waves, not square waves. Square waves have harmonics that would interfere with the test.