Many Plants Flower in Response to Day-Length Cues

Many plants flower in response to day-length cues. Which of the following statements best summarises this phenomenon?

A) As a rule, short-day plants flower in the summer.
B) As a rule, long-day plants flower in the spring or autumn.
C) Long-day plants flower in response to long days, not short nights.
D) Flowering in short-day and long-day plants is controlled by phytochrome.