Prenatal ultrasound is usually performed for five times. They are<br/>( ). A: ultrasonography during early pregnancy (6-8 weeks pregnant) B: ultrasonography at 11-14 weeks pregnant C: ultrasonography at 20-24 weeks pregnant D: ultrasonography at 28-32 weeks pregnant, preclinical ultrasonography

( ) is a noninvasive testing. A: Ultrasonography B: MSAFP C: Maternal Serum Screen D: Amniocentesis