Which of the following does the nurse implement as the most important measure in preventing transmission of harmful pathogens to patients with depressed bone marrow function?

C Strict and frequent handwashing by all people having contact with the patient B Placement of patients in private rooms with high-efficiency particulate air (HEPA) filtration D Administration of combinations of prophylactic antibiotics A Creation of a sterile environment for the patient with the use of laminar airflow rooms