Answer:
C major: no sharps, no flats
F major: no sharps, B flat
Bb (B flat) major: no sharps, B and E flat
Eb major: no sharps; B, E, and A flat
Ab major: no sharps; B, E, A, and D flat
Db major: no sharps; B, E, A, D, and G flat
Gb major/F# (F sharp) major: no sharps; B, E, A, D, G, and C flat / F, C, G, D, A, and E sharp; no flats
B major: F, C, G, D, and A sharp; no flats
E major: F, C, G, and D sharp; no flats
A major: F, C, and G sharp; no flats
D major: F and C sharp, no flats
G major: F sharp, no flats