Experiments Have Shown That When a Short-Day Plant (SDP)and a Long-Day

Experiments have shown that when a short-day plant (SDP) and a long-day plant (LDP) are grafted together and the SDP is exposed to a photoperiod that causes it to flower,the LDP also flowers.This suggests that a specific flower-initiating hormone is produced in plants.A properly controlled experiment would also

A) include grafting together the two plants without inducing the SDP.
B) lengthen the SDP photoperiod.
C) include exposing only the LDP plant to P_fr light.
D) shorten the SDP photoperiod.
E) include an LDP photoperiod.