The Results of Tibbetts and Izzo's 2010 Experiment on Facial

The results of Tibbetts and Izzo's 2010 experiment on facial patterns and the fighting behavior of paper wasps are shown below. Why did Tibbetts and Izzo manipulate the wasps' aggressiveness, in addition to facial pattern?

A) to test whether hormones could artificially alter the fighting qualities of wasps
B) to test whether alteration of facial patterns strengthens the fighting ability of wasps
C) to test whether the alteration of facial patterns would result in increased aggression
D) to test whether the facial pattern is a conventional signal that is kept honest by continuous testing from conspecifics