Because most birds travel through the air at high speeds, they must have

A) a crop and a gizzard.
B) highly sensitive sensory systems.
C) complex songs.
D) eggs and no placenta.
E) a three-chambered heart.

Birds need highly sensitive sensory systems to navigate and find food while flying at high speeds. A crop and gizzard are digestive organs that aid in food processing, but are not necessary for flight. Complex songs and the presence of eggs with no placenta are also not directly related to flight. While birds do have a unique four-chambered heart, it is not accurate to say they must have a three-chambered heart.