Which of the following study designs requires participants to sign an informed consent document?
A. a retrospective chart review that compares ethnicity and cancer treatment outcomes after removing patient personal identifiers
B. a voluntary anonymous survey posted on a support group website for individuals with celiac disease on their experience with genetic testing
C. a prospective randomized trial of asymptomatic BRCA1 mutation positive individuals to evaluate the efficacy of preventive oophorectomy
D. a study to determine what percentage of colorectal cancer tumors diagnosed before age 30 demonstrate microsatellite instability using existing pathology specimens donated to a National Colorectal Cancer Registry