Great question, (A) is a tempting answer choice but this is a "most strongly supported" question, meaning we must be careful not to make any unwarranted inferences. The passage only tells us that the 60% group reported feeling less angry, 70% group reported no difference, and 80% group reported feeling more angry. The only inference we can make here is that that there appears to be some correlation between the intensity of CYCLING and the subsequent mood for PROFESSIONAL cyclists, whereas (A) makes a general statement "the higher the pulse rate attained in sustained exercise..", it is not even talking about cycling or professional cyclists, but any sustained exercise. We cannot possibly make this inference from a single research study of professional cyclists and argue that we would observe the same effect when participants are engaged in a different exercise or when participants are recreational cyclists, for instance. Since (A) makes an unwarranted inference, it is an incorrect answer choice.