A tritone is ...

A. any three notes that, when played together, sound pleasing.

B. a chord consisting of three notes.

C. an interval that played an important part in 12th century music compositions.

D. an interval of three whole steps.

I believe the Answer is letter D.

The correct answer is D. A tritone is an interval of three whole steps.

Explanation:

It is called tritone the interval between heights of two musical notes that has exactly three whole tones. The so-called tritone effect is one of the most complex dissonances possible in western music.

The tritone causes a sensation of movement, which makes it very explored in moments of "tension" of the music.

The tritone is an essential element of some heavy metal groups, composing its characteristic musical atmosphere.