Suppose Lettuce Seeds Are Exposed to a Series of Alternating

Suppose lettuce seeds are exposed to a series of alternating flashes of red light (abbreviated R) and far-red light (abbreviated FR) .(E.g., a flash of red light followed by a flash of far-red light is denoted as R→RF.) Which of the following series of flashes would result in the germination of those seeds?

A) FR only
B) R→FR
C) R→FR →R→FR
D) R →FR→R→FR→R
E) R→FR→R→FR→R→FR