A Nurse States the Purpose of a Research Study As

A nurse states the purpose of a research study as, "This study will compare the effect of warm and cold applications on the resolution of intravenous (IV) infiltrations in hospitalized older-adult patients in the early postoperative period." In this statement, what constitutes the independent variable(s) ?

A) Postoperative older adult patients
B) Early postoperative period
C) Warm and cold applications
D) Resolution of IV infiltrations