Journalist: A recent study showed that people who drink three cups of decaffeinated coffee per day are twice as likely to develop arthritis -- inflammation of joints resulting from damage to connective tissue -- as those who drink three cups of regular coffee per day. Clearly, decaffeinated coffee must contain something that damages connective tissue and that is not present in regular coffee. Which one of the following would be most useful to know in order to evaluate the journalist's argument?
A: whether most coffee drinkers drink more than three cups of coffee per day
B: whether people who exercise regularly are more likely to drink decaffeinated beverages than those who do not
C: whether people who drink decaffeinated coffee tend to drink coffee less often than those who drink regular coffee
D: whether the degeneration of connective tissue is slowed by consumption of caffeine and other stimulants
Choose A, B, C or D as your solution.
D