How many sub layers does the earths layer have

Why are current extinctions of concern to enviromentalists?

Climate like that in the sahara desert have the fastest rates of weathering

Viruses can be transmitted through air, water, food, insect bites, and direct skin contact. once a virus gains entry into the body, it invades a host cell in order to? a. synthesize antibodies for defense b. deactivate the host cell's defenses c. access cell processes for reproduction d. metabolize host proteins and grow