During Administration of a Nebulized Medication Via Face Mask, Which

During administration of a nebulized medication via face mask, which assessment by the nurse is most important?

A) Verifying that the nebulizer produces a continuous mist
B) Ensuring the face mask fits snugly on the client's face
C) Performing the five rights and three safety checks
D) Positioning the client in a semi-Fowler's position