Scientists Interested in Applying the Optimal Foraging Model to Wagtail

Scientists interested in applying the optimal foraging model to wagtail birds' feeding behavior gathered data on the prey (flies) and calories consumed while the prey was being handled (the time the prey is caught until it is consumed) by the wagtails. Which conclusion is supported by this graph?

A) Prey size does not affect the number of calories gained per second of handling time by wagtails.
B) Wagtails get more calories per second of handling time with larger flies than with smaller ones.
C) Wagtails get more calories per second of handling time with smaller flies than with larger ones.
D) Wagtails get more calories per second of handling time with 7-mm flies than with either larger or smaller ones.