Which studies are observational? Select all that apply. A. A worker for the Department of Motor Vehicles compares the age of drivers to the age of the car owned by the driver.
B. A worker for a hospital compares the cholesterol level of patients treated for a heart attack to the patient’s outcome, recovery or death.
C. A researcher used an ice pack to treat migraines for participants in one group and used a standard migraine relief drug with another group
D. A researcher gave one group of dogs food that contained grains and another group of dogs grain-free food and compared how often the dogs in each group scratched their skin.
E. A researcher observed drivers stopping at a toll booth to see if women or men were more likely to be wearing a seat belt.