To make the answers disappear:

• Highlight the words Correct Answer? Frankfurt.
• Click Text>Text Color and select white (top left color).
  Ta-da! The words have disappeared! (Actually, they're still there; but the white text now is hidden by the white fill color of the rectangle you drew earlier.
• Repeat the step above for each answer to the quiz.
• Save your work.
  
  
  Next: Abracadabra!