Many plants flower in response to day-length cues. Which of the ...

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Many plants flower in response to day-length cues. Which of the following statements best summarizes 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 fall.
C) Long-day plants flower in response to long days, not short nights.
D) Flowering in day-neutral plants is only influenced by day length if there is an exceptionally warm spring.
E) Flowering in short-day and long-day plants is controlled by phytochrome.

[clippers!]

I chose E and got the answer, hope that helps.