Which of the following correctly sets off a quotation?
Select one: A. As Frederick Douglass once said, “If there is no struggle, there is no progress.” B. Frederick Douglass once said that: “If there is no struggle, there is no progress.” C. As Frederick Douglass once said: “If there is no struggle, there is no progress.”D. Frederick Douglass once said that, “If there is no struggle, there is no progress.”