Which statement about population exposure to nicotine from environmental tobacco smoke is TRUE?

Detectable nicotine exposure among nonsmoking Americans declined between 1988 and 2008.

Detectable nicotine exposure among nonsmoking Americans roughly doubled between 1988 and 2008.

Nicotine exposure trends among nonsmokers show no change from 1988 to 2008.

Nicotine exposure among nonsmokers increased only in rural populations while decreasing in urban populations between 1988 and 2008.