Teenage Research Unlimited, a market research firm in Northbrook, Ill., projects that the 31.6 million Americans from ages 12-19 will spend $108 billion of their own money in 2000, along with $47 billion of their family's funds. They also account for a disproportionately large share of consumer spending. Households with one or more teen-agers spend $10,000 more per year than those without any. And with parents working more than ever before, teens have assumed greater influence in household decision-making.

What is the central idea of this passage?

A. Market research firms are interested in what teen-agers have to say.
B. In families with working parents, teen-agers affect decision-making.
C. Teen-agers account for billions of dollars of consumer spending every year.
D. Households with teen-agers spend more than those without any teen-agers.