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

How is ribosomal rna useful as a molecular clock? a. a large portion of the dna ring is not vital to structure or function, allowing it to accumulate neutral mutations. b. its rate of mutation increases over time as organisms continue to evolve and differentiate from each other. c. a slow mutation rate makes it useful for determining evolutionary relationships between ancient species. d. it is only found in select organisms, making it easier to compare relationships between species that have it.

Which of the following particles always has a positive charge? a. electronb. neutron c. proton d. ion

What organ is the first to receive nutrients that have been absorbed from the digestive tract?