Arthropods have an exoskeleton made of

chitin

cellulose

silica

cartilage

chitin

Explanation:

An arthropod is an invertebrate animal that exhibit an exoskeleton that can be define as an external outer covering of the animals. The exoskeleton in the arthropods is made up of chitin. The hard outer exoskeleton plays many roles like it provides the protection to the animal against the predator, any environmental hazard and it is waterproof which means it does not allow the entrance of external water inside the body cover of the animal.

human didn't come from monkeys man i hate these stupid teachers

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.