If Carly has dual citizenship, and its already mentioned that she has Canadian citizenship, then the third statement is true because it provides the second citizenship (An American one). To break it down, in order for the first statement to be true "Carly has dual citizenship" then both statements 2 qnd 3 are true. In order to have a dual (in simple terms it means two) citizenship then statement 3 of "Carly has American and cCanadian citizenship" must be true.
