Answer:
A
Step-by-step explanation:
The diatonic scale consists of seven notes, namely C,D,E,F,G,A,B (C major scale) on a Keyboard, these notes are the white ones. The black and white ones on the keyboard scales are called Chromatic scale.
A scale besides having seven notes, it must have 5 tones intervals and 2 half tones (E-F and C-B, for the C major scale)
As the note after B, is C. And the C major scale is completely diatonic, and also a frequency does it's not only related to C scale. The answer is A.