Which rhetorical device makes the situation less serious than it is?

A. ad hominem
B. understatement
C. overstatement
D. ethos

What reasons does the speaker provide to support his viewpoint or claim in what to the slave is the fourth of july i read to speech and but i just don't fully understand the question i just want to make sure i get it right so to explain that the question is asking me to do. and you!