Part A: Dramatic irony occurs A. when the audience knows something a character does not.
Part B: Without the specific passage referenced in the options, I can't definitively identify which line is an example of dramatic irony. However, typically, a line that suggests a character is unaware of a crucial fact that the audience knows would be the best choice. If you provide the passage or context for the dialogue, I would be able to help identify the example of dramatic irony.