Which of the following statements is correct with regards to a ...

[xclash]

Which of the following statements is correct with regards to a "circadian rhythm" in plants?
A) It may have the same signal transduction pathway in all organisms.
B) Once set, it cannot be changed.
C) It works independently of photoperiodic responses.
D) Once set, it is independent of external signals.
E) It can be changed to a longer or shorter period by altering the light quality.

[clippers!]

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