The answer for this should be D. (A, B, C#)
All major scales have the same pattern, which is 2 whole tones, one halftone, 3 more whole tones, and another halftone.
Just a reminder, whole tones are where two notes that can be separated by another note in half. Examples of whole tones are C to D (can be separated by C#), F to G (can be separated by F#), and B to C# (separated by C, as there's nothing called B#).
Special cases of halftones include B to C, and E to F, you can see there are no black keys between these notes in a regular piano.
Therefore, we can use the pattern to find the remaining notes. According to the pattern, the note behind G and G itself should make a whole tone, so, the missing note should be A. Now again, the next one makes a whole tone with A too, so it should be B. Next one, again, another whole tone, but since there's no B#, so the note that makes a whole tone with B should be C#. And lastly, a halftone, which would be D, which is given in the question.
Therefore, the answer should be D.
