[单项选择]All life on the earth ______ off the sun.
A. depends
B. carries
C. keeps
D. goes

[单项选择]All life on the earth ______ on the sun.
A. depends
B. carries
C. keeps
D. goes

[单项选择]For three quarters of its span on Earth, life evolved almost ______ as microorganisms.
A. precisely
B. instantly
C. initially
D. exclusively

[单项选择]Scientists believe that when life on earth began, the earth atmosphere consisted of ___________.
A. oxygen and nitrogen
B. hydrogen, oxygen and nitrogen
C. hydrogen and its compounds
D. hydrogen, oxygen and their compounds

[单项选择]Students learning about how life began on Earth may be presented with the perplexing question, "Which came first, the chicken or the egg"
A. pressing
B. puzzling
C. patronizing
D. penetrating

[单项选择]Canada will {{U}}prohibit{{/U}} smoking in all offices later this year.
A. ban
B. remove
C. eliminate
D. expel

[单项选择]The history of life on earth has been a history of between living things and their surroundings.
A. interaction
B. intersection
C. interference
D. intercourse

[单项选择]Life as we know exists on the earth because the atmosphere _________.
A. contains a layer of ozone gases.
B. about 42 degrees colder than on the ground.
C. 21% oxygen by weight.
D. less than 1% of xenon by volume
E. about 75 degrees colder than in Interlaken
F. is warmed by the earth’s heat.

[单项选择]The Earth is in trouble because of all the following EXCEPT ______.


A. dirty roadside
B. sick plants and animals
C. unhealthy water
D. poisonous air

[单项选择]

All the useful energy at the surface of the earth comes from the activity of the sun. The sun heats and feeds mankind. Each year it (21) men with two hundred million tons of grain and (22) ten million tons of wood.
Coal, oil natural gas, and all other (23) are stored-up energy from the sun. It was collected by the plants as carbon compounds and stored (24) ago.
Even waterpower comes from the sun. Water (25) into vapor by the sun falls as rain. It runs (26) the mountains and is converted to electric power.
Light transmits only the energy (27) comes from the sun’ s outer layers, and (28) of this energy that is directed toward the earth never arrives. About (29) of it is absorbed by the atmosphere of the earth. In (30) ,the earth itself gets only one half-billionth of the Sun’ s entire output of rediant energy.

28（）
A. turns
B. turning
C. turned
D. is turned