Which of the following statements is true regarding the different conditions that pose threats for newborns?

a. Small for date infants weigh less than 5.5 pounds at birth.
b. Low birth weight babies weigh between 6 and 7 pounds.
c. Small for date infants have a below-normal weight when the length of the pregnancy is considered.
d. Low birth weight babies weigh less than 90 percent of all babies of the same gestational age.