The correct answers are:
Greek theaters had a circular or semicircular stage called an orchestra. Indeed, that was the circular space where the chorus sang and danced to provide additional layers of interpretation and emotional intensity to the plays. The orchestra measured roughly 78 feet.
Only men could be actors, even when characters in a play were female. True, although it appears that there were some exclusively female theater festivals where women could attend and watch other women play the parts of a goddess.
Women formed a chorus that sang behind the actors. True but only for dramas where the main character was a woman (Aeschylus, Suppliant Women, Euripides, Bacchae, Euripides, Electra, Euripides, Iphigenia in Tauris).
The Greeks did not want to feel sad at the theater. False. They loved tragedies, and they invented Greek Tragedy for that reason.