Which of the Following Statements Is a Fact, Rather Than

Which of the following statements is a fact, rather than an inference or opinion?

A) Dr. King's "I Have a Dream" speech was the greatest speech he ever gave.
B) No one had a greater impact on the civil rights movement than M. L. King.
C) James Earl Ray should have been executed for killing Martin Luther King.
D) Martin Luther King won the Nobel Peace Prize in 1964.