Simone wrote the following geometric statement. The diagonals of a parallelogram are congruent.
Then Simone drew a parallelogram in which the diagonals had different lengths. Which statement BEST describes what Simone did?

A She stated a theorem, then used a postulate to show that the theorem is true.
B. She stated a theorem, then used a postulate to show that the theorem is false.
C. She made a conjecture, then used an example to show that her conjecture is true,
D. She made a conjecture, then used a counterexample to show that her conjecture is false.