A double-blind, randomized study is being used to test the effectiveness of a new drug that targets the multi-drug resistant bacterium Clostridium difficile. Infected participants in the study were given either a placebo or the test drug and then monitored for one month for clearance of infection. This type of study can best be characterized as a(n). A. observational study
B. cross-sectional study
C. Correlation study
D. experimental study