If a short-day plant has a critical night length of 15 hours,then which of the following 24-hour cycles will prevent flowering?

A)8 hours light/16 hours dark
B)4 hours light/20 hours dark
C)6 hours light/2 hours dark/light flash/16 hours dark
D)8 hours light/8 hours dark/light flash/8 hours dark
E)2 hours light/20 hours dark/2 hours light