Who is credited with first creating dialogue on stage?
a. dionysus
b. thespis
c. sophocles
d. aristotle

I believe this would beThespis considering he was the first person to walk onto a stage and actually portray someone other than himself.  Being the first actor, he actually delivered the first dialogue uttered.  Prior to Thespis, the stage performance consisted of various people telling or relaying a story.  Dialogue, or speech was first used or delivered in a play considered blasphemous at the time as he delivered lines spoken by God. 

Ethos