Speech balloons, also known as speech bubbles, dialogue balloons or word balloons, are a graphic convention used most commonly in comic books, comics and cartoons to allow words to be understood as representing the speech or thoughts of a given character in the story or events of the graphic novel or Comic.
According to the information presented before I would conclude that the main purpose of a speech bubble in a graphic novel is:
D) It illustrates internal thoughts.
If it's just a random thesis:
Topic: Dog Fights
Thesis: Dog fights should be illegal, since they are a cruel way to abuse dogs for profit.
Opposing Thesis: Dog fights are entartaining, and should be continued.
Suffix (able)
Meaning; suitable for or worth quoting.
