How is renewable fuel use expected to change in the next decade? a. it is expected to decrease. b. it is expected to increase. c. it is expected to fluctuate. d. it is expected to remain the same.

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