Laboratory studies contribute to scientific research because an experimenter can exert ____________, while field studies allow researchers to observe behaviors in the ____________ in which they occur

A controlled study of sex education in the United Kingdom found that whether or not an adolescent becomes sexually active depends more on family, peers, and culture than on information from sex education classes

Indicate whether this statement is true or false.

Randi is pregnant for the first time. Given the frequency with which twins and triplets have occurred in her family, she is understandably concerned that she will have a multiple-birth pregnancy. If you were her gynecologist, which of the following prenatal tests would you recommend to either confirm or rule out the number of babies she is carrying?

a. quadruple maternal blood test b. amniocentesis c. chorionic villus sampling d. ultrasound