A student placed 20 tobacco seeds of the same species on moist paper towels in each of two petri dishes. Dish A was wrapped completely in an opaque cover to exclude all light. Dish B was not wrapped. The dishes were placed equidistant from a light source set to a cycle of 14 hours of light and 10 hours of dark. All other conditions were the same for both dishes. The dishes were examined after 7 days, and the opaque cover was permanently removed from dish A. Both dishes were returned to the light and examined again at 14 days. The following data were obtained:
Which of the following best supports the hypothesis that the difference in leaf color is genetically controlled?
a. the number of yellow-leaved seedlings in dish A on day 7
b. the number of germinated seeds in dish A on days 7 and 14
c. the death of all the yellow-leaved seedings
d. the existence of yellow-leaved seedlings as well as green-leaved ones on day 14 in dish B