What geographic obstacles make securing the border between the us and mexico difficult?

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.

From the standpoint of geography,a is an internal rendering of an individual's known world

What statement about charlemagne is not true? a. charlemagne's empire collapsed during his rule b. charlemagne sent missionaries throughout europe c. charlemagne encouraged the arts and education d. charlemagne ruled much of western europe a. charlemagne's empire collapsed during his rule