A genetic defect in enzymes that cause retardation is:

Very young children tend to breathe predominantly with their diaphragm because:

A. their chest wall and ribs are very pliable. B. they require less tidal volume per breath. C. their intercostal muscles are not fully developed. D. there is no nerve innervation of the intercostal muscles.

The fetus is potentially viable if born at the end of which stage of development?

a. Alveolar b. Canalicular c. Pseudoglandular d. Saccular