Explanation:
We can see a pattern beginning to emerge. G major is built on scale degree 5 of C major and has one sharp (F#). D major is built on scale degree 5 of G major and has two sharps (F#) and (C#). We could continue the pattern by building a major scale on scale degree 5 of D major (A) and would arrive at A major, which has three sharps (F#, C#, and G#).
