Only One of the Following Students Is Definitely Engaging in Critical

Only one of the following students is definitely engaging in critical thinking. Which one?

A) Louise has a puzzled look as she reads her textbook. "I don't understand what the author is trying to say," she thinks.
B) Sam reads over his responses to the essay questions on an astronomy test. "I think I've done my best," he tells himself. "I'm pretty sure I answered the first two questions correctly, but I'm not so sure how well I did on the last question."
C) As Morgan watches her lab partner experiment with a pendulum, she says, "You just changed the length of the string at the same time you added more weight. That won't tell us anything."
D) Raul jumps at the chance to learn how to use desktop publishing software. "I'm particularly interested in learning how to integrate text and graphics," he tell his teacher.