4. Which is a true statement regarding preterm labor?
a. A woman who has had previous preterm labor has lower risk of preterm labor.
b. Behaviors such as smoking, illegal drug use, alcohol consumption, and lack of prenatal care are all maternal risk factors.
c. High socioeconomic status and white race are two factors increasing the risk of preterm labor.
d. Women between the ages of 18 and 40 are at greater risk of preterm labor.