Why do people in Africa wear masks

All of the following statements about the biosphere are true except: a. light and heat from the sun do not affect the biosphere. b. the biosphere gets resources from earth's crust, hydrosphere and atmosphere. c. like "biology", the name for the biosphere comes from the greek word for life. d. the biosphere includes all living organisms on earth's surface.

What body of water is the second cataract of the nile river submerged under

In the diagram below, ab and bc are tangent to o. what is the measure of