Scarlet Gilia (Ipomopsis Aggregata) Usually Has Red Flowers in an Inflorescence

Scarlet gilia (Ipomopsis aggregata) usually has red flowers in an inflorescence of up to 250 flowers. In certain populations in the Arizona mountains, however, the flowers range from red to pink to white. In early summer, most (but not all) of the flowers were red. Six to eight weeks later, the same individual plants were still present; the flowers ranged from pink to white, and few red flowers were present. The major pollinators early in the season were two species of hummingbirds active during the day; they emigrated to lower elevations, and the major pollinator later in the season was a hawk moth (a type of moth) . The hawk moth was most active at sunset and later, and it preferred light pink to white flowers after dark. When hummingbirds were present, more red flowers than white flowers produced fruit. When only hawk moths were present, more white flowers produced fruit. (K. N. Paige and T. G. Whitham. 1985. Individual and population shifts in flower colour by scarlet gilia: A mechanism for pollinator tracking. Science 227:315-17) .
-Which of the following proposed controls would be most appropriate for the experiment when, late in the season, scientists painted some of the red flowers white?

A) Some red flowers should be painted pink.
B) Some red and light coloured flowers should be covered to prevent pollinator access.
C) Plants with light and dark coloured flowers should be fertilised.
D) A necessary control would be to put red paint on some of the red flowers in order to control for the effects of paint.