The correct options are
A vmax=±ωA, at mean position
B amax=±ω2A, at extreme position
C amin=0, at mean position
D vmin=0, at extreme position
Velocity-Displacement relationship
v=±ω√A2−x2
⇒vmax=±ωA at x=0→ Mean position.
& vmin=0 at x=A→ Extreme position.
Acceleration-Displacement relationship
a=−ω2x
⇒|amax|=ω2A at x=±A→ extreme position.
& |amin|=0 at x=0→ Mean position.
Hence, options (a), (b), (c) and (d) are correct.