In Patients with ALS,positive Pressure Noninvasive Ventilation

In patients with ALS,positive pressure noninvasive ventilation

A) is recommended once vital capacity falls below 50% of predicted values.
B) is recommended at diagnosis to prevent vital capacity from decreasing.
C) is not recommended,as supplemental oxygen is usually all that is needed.
D) is not recommended,as it cannot stop progression of disease and will extend the patient's survival only by a few months.