Maeko was nervous about the ________. She knew it was likely to be the largest expense in the advertising budget.

A) publicity plan
B) media flight plan decision
C) media mix choice
D) media buy
E) monitoring and evaluation plan decision

Maeko's nervousness about the expense suggests that she is focused on the financial aspect of advertising. Among the options presented, the only one directly related to cost is the media buy, which involves purchasing advertising space or time. The other choices, such as publicity plan and monitoring and evaluation plan, are more focused on strategy and analysis rather than budgeting. The media mix choice and media flight plan decision are related to the specific channels and timing of advertising rather than the cost. Therefore, the best choice for Maeko's concern about expense is a media buy.