Having Misplaced a Stethoscope, a Nurse Borrows a Colleague's Stethoscope

Having misplaced a stethoscope, a nurse borrows a colleague's stethoscope. The nurse next enters the patient's room and identifies self, washes hands with soap, and states the purpose of the visit. The nurse performs proper identification of the patient before auscultating the patient's lungs. Which critical health assessment step should the nurse have performed?

A) Running warm water over stethoscope
B) Draping stethoscope around the neck
C) Rubbing stethoscope with betadine
D) Cleaning stethoscope with alcohol