Choose the best answer.

1		The most abundant gas in the earth's atmosphere is _________________.
			A)	oxygen
			B)	carbon dioxide
			C)	nitrogen
			D)	argon
2		The layer of the atmosphere in which weather occurs is the _______________.
			A)	mesosphere
			B)	stratosphere
			C)	thermosphere
			D)	troposphere
3		The atmosphere constituent chiefly responsible for absorbing ultraviolet radiation from the sun is ________________.
			A)	carbon dioxide
			B)	water vapor
			C)	ozone
			D)	helium
4		When saturated air is cooled, ______________.
			A)	it becomes able to take up more water vapor
			B)	some of its water content condenses out
			C)	the relative humidity goes down
			D)	convection currents result
5		Clouds consist of _______________.
			A)	water droplets at all altitudes
			B)	ice crystals at all altitudes
			C)	water droplets at low altitudes and ice crystals at high altitudes
			D)	ice crystals at low altitudes and water droplets at high altitudes
6		Clouds occur when moist air is cooled by _______________.
			A)	expansion when it rises
			B)	expansion when it falls
			C)	compression when it rises
			D)	compression when it falls
7		The term greenhouse effect is used to describe the _________________.
			A)	condensation of moisture to form dew
			B)	conversion of carbon dioxide to oxygen by green plants
			C)	heating of the atmosphere by direct solar radiation
			D)	heating of the atmosphere by infrared radiation from the earth
8		The seasons occur as a result of ________________.
			A)	variation in the sun's energy output
			B)	variation in the distance between the earth and the sun
			C)	variations in the orbital speed of the earth
			D)	the tilt of the earth's axis
9		Winds form in response to the _________________.
			A)	uneven heating of the earth's surface
			B)	rotation of the earth on its axis
			C)	coriolis effect
			D)	friction between ocean currents and the atmosphere
10		Because of the coriolis effect, a wind in the northern hemisphere is deflected ___________________.
			A)	upward
			B)	downward
			C)	toward the right
			D)	toward the left
11		An airplane flies at the same speed relative to the air at a high altitude from New York to Paris and back.
			A)	The New York to Paris flight takes less time.
			B)	The Paris to New York flight takes less time
			C)	The two flights take the same time on the average.
			D)	Any of the above, depending on the season
12		A cyclone is a weather system centered about a ________________.
			A)	region of low pressure
			B)	region of high pressure
			C)	hurricane
			D)	cold front
13		The winds in an anticyclone _______________.
			A)	blow directly toward its center
			B)	spiral toward its center
			C)	blow directly away from its center
			D)	spiral away from its center
14		Unstable weather is associated with _________________.
			A)	cyclones
			B)	anticyclones
			C)	trade winds
			D)	the greenhouse effect
15		The chief reason why the equatorial regions are warmer than the polar regions is that _________________.
			A)	the equator is closer to the sun
			B)	sunlight falls more nearly vertically on the equatorial regions
			C)	sunlight is reflected by ice and snow in the polar regions
			D)	the is more CO2 in the air over the equatorial regions
16		Ice ages ________________.
			A)	cover the entire earth with a sheet of ice
			B)	freeze all the oceans
			C)	occurred seldom in the past
			D)	occurred frequently in the past
17		The approximate percentage of the earth's surface covered by water is ___________________.
			A)	10 percent
			B)	50 percent
			C)	70 percent
			D)	90 percent
18		Compared with the average height of the continents above sea level, the average depth of the ocean basins below sea level is _______________.
			A)	smaller
			B)	greater
			C)	about the same
			D)	sometimes smaller and sometimes greater, depending upon the tides
19		Most surface ocean currents are due to ________________.
			A)	melting glaciers
			B)	rivers
			C)	winds
			D)	differences in the altitude of the ocean surface
20		The Gulf Stream is a ________________.
			A)	warm current in the North Atlantic
			B)	cool current in the North Atlantic
			C)	river that flows into the Gulf of Mexico
			D)	warm wind blowing over the North Atlantic