The Evidence That Smoking Causes Lung Cancer Is Very Strong

Multiple Choice

The evidence that smoking causes lung cancer is very strong. But it is not the strongest possible statistical evidence because

A) we can't do experiments to compare smokers and non-smokers.
B) only smokers have been studied.
C) the studies of the effects of smoking are not double-blind.
D) all the studies of the effects of smoking involve animals, not humans.