For the Past 3 Months,the Nurse Has Been Exchanging New

For the past 3 months,the nurse has been exchanging new needles for used needles at a homeless shelter frequented by drug users.How might the nurse know whether his or her time and effort were effective?

A) More people came each night with used needles,asking to exchange them.
B) The local health department reported a downward trend in newly diagnosed human immunodeficiency virus (HIV) infection.
C) Persons who stayed at the shelter frequently expressed appreciation to the nurse.
D) The staff of the homeless shelter stated that they had been serving fewer clients.