An infant may be more at risk of sudden infant death syndrome if he or she ______.

A) sleeps only in a crib
B) sleeps on the back
C) is older than 5 months
D) is exposed to tobacco smoke

Research has shown that exposure to tobacco smoke (either through maternal smoking during pregnancy or environmental smoke exposure after birth) can increase the risk of sudden infant death syndrome (SIDS). Sleeping on the back has been recommended as a preventive measure for SIDS, but it is not the only factor that affects the risk. Sleeping only in a crib can actually lower the risk by reducing the chance of accidental suffocation, while the age of the infant alone is not a significant risk factor for SIDS.