Red wine contains flavonol, an antioxidant thought to have beneficial health effects. But to have an effect, the antioxidant must be absorbed into the blood. The article "Red Wine is a Poor Source of Bioavailable Flavonols in Men" (The Journal of Nutrition [2001]: 745-748) describes a study to investigate three sources of dietary flavonol-red wine, yellow onions, and black tea-to determine the effect of source on absorption. The article included the following statement: We recruited subjects via posters and local newspapers. To ensure that subjects could tolerate the alcohol in the wine, we only allowed men with a consumption of at least seven drinks per week to participate . . . Throughout the study, the subjects consumed a diet that was low in flavonols.
a. What are the three treatments in this experiment?
b. What is the response variable?
c. What are three extraneous variables that the researchers chose to control in the experiment?