13. The differences between two molecules include the type of sugar that forms a section of the molecules and the identity of one of the four
nitrogenous bases that make up another section of the molecules. These
two molecules are - *

Abird flies by moving its wings up and down. which two systems are most directly responsible for the movement of a bird's wings? a. skeletal and muscular systems b. respiratory and muscular systems c. skeletal and digestive systems d. respiratory and digestive systems