3. Select the cross-sectional study from the options below.
||A scientist examines the effect of caffeine on
the athletic performance of endurance athletes. 20 experimental
subjects drink coffee prior to exercise and their performance
is compared to 20 control subjects who drink a placebo prior
||A scientist investigates the relationship between
vegetarianism and athletic performance by placing 2 individuals
on a vegetarian diet and their examining their level of fitness.
||A scientist wants to investigate the relationship
between smoking and heart rate. The heart rates of 200 individuals
are measured; the heart rates of smokers and compared to those
||A scientist wants to examine the influence of
anabolic steroids on the liver functions of athletes. 15 experimental
subjects are given anabolic steroids and 15 control subjects
are given a placebo; the liver functions of the two groups are