Which of the following is an example of physiological preconditioning?

Physiological preconditioning is something that must come before or is necessary to a subsequent physiological result. Photoperiodism is the phenomenon of physiological changes that occur in plants in response to relative length of day and night. The response of the plants to the photoperiod expressed in the form of flowering is also called as photoperiodism. The phenomenon of photoperiodism was first discovered by Garner and Allard in 1920. Plants have been classified into long day, short day and neutral plants according to photoperiodism.