The argument concludes that complexity of chocolate flavor masks any difference in taste due to the lack of fat. (C) tells us that the more distinct compounds required to produce a flavor, the better people like it. (C) has no impact on the validity of the conclusion because the argument is not saying that people prefer chocolate over vanilla, but that they tend to have no preference when it comes to low-fat versus full-fat ice cream options, and the number of distinct compounds -500 to be exact - is the same for a full-fat or low-fat chocolate ice cream option.