The stimulus presents an argument, as follows: C: A recent study reveals that TV ads do not significantly affect kids' preferences for breakfast cereals. P: The study compared 2 groups of kids. P: One group watched no TV. P: The other watched average amounts of TV and TV ads. P: Both groups strongly preferred the sugary cereals heavily advertised on TV.
From the fact that both groups strongly preferred the same cereals, the author of the stimulus concludes that TV ads don't affect kids' cereal preferences.
Answer choice (A) weakens this argument by explaining that kids who watch zero TV are influenced by kids who do watch TV. If this is true, then a kid might prefer heavily advertised cereal even if that kid herself doesn't watch TV ads.