Which of the following statements is true about sudden infant death syndrome (SIDS)?
a. Its level of risk is high at 36 to 48 months of age for infants.
b. It usually occurs when infants stop breathing, usually during night, and die suddenly without any apparent reason.
c. It is the least common cause of infant deaths in the United States.
d. Its level of risk is high when infants sleep on their backs, in a supine position.