The nurse provides care for a school-age child brought to the clinic by the parent. The parent is concerned because the child has a temperature of 103°F (39.3°C), has vomited twice, and slept all day yesterday. The child reports, "light hurts my eyes" and also reports headache and nausea. The nurse observes the child has a petechial rash on the trunk of the body. Which assessment is most important for the nurse to perform?

A. Grasp the child's hands and ask the child to squeeze the nurse's hands.
B. Stroke the plantar surface of the child's foot with a reflex hammer.
C. Gently flex the child's head and neck onto the chest.
D. Have the child stand with eyes closed, arms at the sides, and the feet and knees close together.