In C major, what are the notes that make up an It +6 chord?

An It +6 chord is a type of augmented sixth chord that typically resolves to the dominant chord. In the key of C major, this chord is built from the major sixth scale degree (A) and raises the fourth scale degree (C) while also including a lowered seventh scale degree (A#).

In this case, the notes of the It +6 chord in C major are C, E, and A#. This chord functions as a pre-dominant harmony leading to a G major chord, which is the dominant of C major. The augmented sixth interval is created between A# and F, which is derived from the scale degrees relating to the chord's resolution pattern.

The other options do not form a proper It +6 chord in C major due to the absence of the necessary intervals or incorrect pitches. Therefore, the listed combination of notes in option A effectively represents the It +6 chord, making it the correct choice.