How much oxygen is contained in the atmosphere?
OA) 20%
OB) 21%
OC) 22%
OD) 23%

B~ 21%

What is the main reason that attitudes are more often revealed in spoken rather than written language? a. in writing, we try to put the "best face" on what we write. b. we speak far more often than we write. c. in writing, we can more easily conceal our attitudes. d. in spoken language, we are often careless in our use of words.

Where is the nictitating membrane found? a. between the eyelid and the eyeball b. between the retina and the optic nerve c. between the outer and middle ear d. in the organ of corti in the middle ear

Why do mountaineers become breathless as they reach high altitudes