Protein signatures are preferred over biomarkers for early cancer screening because select one: a. protein signatures are composed of entire sets of proteins, therefore they are less likely to result in false negatives. b. biomarkers are single proteins, therefore they are more likely to result in false positives. c. protein signatures do not have to be secreted into body fluids to be detected. d. biomarkers cannot be used to detect common cancers such as ovarian or prostate cancer.