单选题 Mr. Smith has had a cast applied to his arm as an outpatient in the emergency room. Which of the following home care instructions should the nurse advice for his cast care?
A. Use a ruler to reach inside and scratch under the cast.
B. Apply a heating pad to the arm for 24 hours after the injury.
C. Use powder on the skin around the cast.
D. Smell the cast for foul odors.