Final answer:
The nurse's evaluation of effective relaxation therapy is supported by a decreased heart rate in the patient.
Step-by-step explanation:
The correct answer is c. Decreased heart rate. When a nurse teaches a patient relaxation techniques to decrease stress, one of the expected effects is a decrease in heart rate. This is because relaxation techniques such as deep breathing and guided imagery activate the parasympathetic nervous system, which promotes a state of calmness and reduces heart rate. The other options, such as dilated pupils, increased blood sugar, and elevated blood pressure, are not indicative of effective relaxation therapy.