Final answer:
An infant throws out her arms and legs when she loses support and feels like she is falling due to the startle reflex, also known as the Moro reflex.
Step-by-step explanation:
An infant throws out her arms and legs when she loses support and feels like she is falling due to the startle reflex. This reflex is also known as the Moro reflex and is present in infants from birth until about three or four months of age. It is an instinctive behavior triggered by a sudden loss of support.