1. The correct answer is characters.
Characters are those people who are played by actors on stage. Actors say the lines that are written in the play, trying to convey the same feelings and emotions the characters in the play would evoke in a reader. Chorus refers to a group of people within a play who comment on the events within it; stage directions are instructions for both the actors and those who set the stage; extras are those actors who are not that relevant for the play/movie/show, etc.
2. The correct answer is dialogue.
Dialogue refers to the speech spoken by two or more people; when they are conversing, they are having a dialogue (a monologue would be spoken by one person only). The lines that those actors say in a play are also referred to as the dialogue. Scene is just a part of a play where something happens; script refers to the actual text of the play; dramatis personae is just a Latin term for characters within a play.
3. The correct answer is script.
Like already stated, script is the text of the play, the lines that the characters/actors actually say. Tragedy is an entire genre of plays characterized by a sad ending; prologue is the introduction to a play; line is just a line - it doesn't refer to the entire text or a set of lines.