If a long-day plant has a critical night length of 9 hours,which 24-hour cycle would prevent flowering?

A)16 hours light/8 hours dark
B)14 hours light/10 hours dark
C)15.5 hours light/8.5 hours dark
D)4 hours light/8 hours dark/4 hours light/8 hours dark
E)8 hours light/8 hours dark/light flash/8 hours dark