(A) shows that the children who hadn’t watched any television could have been indirectly influenced by the television ads. This is an alternate hypothesis that could explain the study results, so it weakens the author’s argument.

The fact that it’s possible for something like television advertising to influence preferences does nothing to suggest that it did influence preferences. This does not provide any information that impacts the argument.

It doesn’t matter if these children were already familiar with the advertisements, because they would have become familiar during the experiment. It doesn’t matter when they were exposed to the ads; we only care if they were influenced by these ads.

This provides further information to suggest that advertisements don’t successfully impact children’s preferences. This agrees with the argument’s conclusion and does not weaken the argument.

The argument is about children’s preferences, so this information about adults is irrelevant to the argument and does not weaken it.