The correct answer is choice A. Administer oxygen.

The client is experiencing signs of pulmonary edema, which is a complication of gestational hypertension.

Oxygen therapy can help improve oxygenation and reduce the workload of the heart.

The nurse should also monitor the client’s vital signs, urine output, and magnesium sulfate level.

Choice B. Assess blood pressure.

This is an important action, but not the first priority.

The nurse should assess blood pressure after administering oxygen and stabilizing the client.

Choice C. Assess for visual disturbances.

This is a symptom of severe preeclampsia, but not an immediate threat to the client’s life.

The nurse should assess for visual disturbances as part of the ongoing evaluation of the client’s condition.

Choice D. Assess for proteinuria.

This is a diagnostic criterion for preeclampsia, but not a priority action in this situation.

The nurse should assess for proteinuria as part of the routine urinalysis.

Normal ranges for blood pressure are less than 140/90 mm Hg, and for proteinuria are less than 300 mg/24 hours.