Cathy Examined the Effect of Different Teaching Methods on Students

Multiple Choice

Cathy examined the effect of different teaching methods on students' exam performance. She randomly assigned college students to listen to one of three lectures and then tested them over the material. As hypothesized, she found that students taught by Method 1 earned significantly higher exam grades than students taught by Method 2 or Method 3. Which of the following is the best conclusion to draw from these results?

A) Because Cathy has not done an experiment, she should not draw any cause-and-effect conclusions.
B) Cathy has proven that Method 1 is superior to Method 2 and Method 3.
C) Cathy's results supported the hypothesis.
D) Cathy's study has high external validity.