The figure shows fossilized and living stalk-eyed flies from the family Diopsidae. In fossils, the eye spans of the flies are much smaller than those of living flies.

Which question would BEST help determine whether the change in eye span in stalk-eyed flies was influenced by natural selection?
a. is the eye span of male stalk-eyed flies similar to that of female flies?
b. what is the relationship between the body length and eye span of stalk-eyed flies?
c. how does the eye span of stalk-eyed flies compare from one generation to the next?
d. do fossilized stalk-eyed flies have a shorter body length than living flies?