A mother brings her 15-month-old male child to the ambulatory care clinic for well-child care. He’s crying and pulling at his left ear, which appears erythematous. Which of the following actions should the nurse take first
A. Ask the mother to leave the room because her anxiety is increasing the child’s distress.
B. Examine the ear with the child supine because this aids visualization of the tympanic membrane.
C. Examine the affected ear last in order to minimize distress early in the examination.
D. Examine the left ear first in order to assess what may be physically wrong with the chil
沿向量l=xi+yj的方向导数为（）。