Which of the following statements about the female hymen is correct?
a. all hymens cover the vaginal introitus to approximately the same degree.
b. the first time a female has intercourse her hymen will inevitably tear and cause bleeding.
c. most hymens have at least one opening to allow for the passage of menstrual blood.
d. an imperforate hymen is one which is virtually absent.

What was piaget's explanation as to why preschool-age children in the preoperational stage make errors on tasks requiring conservation? a) preschool children's tendency toward centration prevents them from focusing on other relevant features of a situation b) preschool children have not yet developed numerical understanding; therefore, different amounts are meaningless c) preschool children's neural-visual network is not fully matured d) preschool children have not lived long enough and accrued enough experience to know the difference between quantities