Correct answer choice is:
D. Chord tones.
Step-by-step explanation:
A chord tone is simply a note that subsists inside a specific chord. So, for example, the chord of C major is tendered from 3 notes – C, E, G – they have named the "chord tones".
The primary notes of a 7th chord are the origin, 3rd, 5th, and 7th. Tones so as 9ths, 11ths, and 13ths are associated to as upper extensions and are not supposed primary chord tones (although all are tones that can be practiced in the chord). So the chord tones of a C primary triad are C, E, and G.