A physiological response of plants to the duration of light and darkness is Daily phase cycle, Biological clock, Circadian rhythms, Photoperiodism

The plants in order to flower require a certain photoperiod i.e., the relative length of day and night. The response of plants to the photoperiod, expressed in the form of flowering is called photoperiodism. Short day plants flower when the night lengths exceed their critical photoperiod. They cannot flower under short nights. They need a continuous period of darkness before flowering. In contrast, long day plants flower when night length falls below their critical photoperiod. They cannot flower under short days or long nights. So, the correct answer is option D.