What major muscle is this man contracting to push himself up while doing a push-up?

What substance is the most acidic. lemon juice. tomato juice. sodium hydroxide. water

What part of the cell does 9 represent? a. cytoplasm b. lysosome c. ribosome d. centrosome

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