In a volume of air near Earth's surface today, ____ occupies 78 percent and ____ nearly 21 percent
a. ?nitrogen; oxygen
b. ?hydrogen; oxygen
c. ?oxygen; hydrogen
d. ?nitrogen; water vapor
e. ?hydrogen; helium
ANSWER: a
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Indicate whether the statement is true or false
During the 1950s land ownership was abolished and collectives were established to be followed by the creation of People's Communes in China. The result:
A) Increased productivity led to export surpluses. B) Land dedicated to vegetables and fruits, much of it converted from grain fields, increased 393 percent. C) The per capita consumption of meat in China increased from 12 pounds to 62 pounds. D) The deaths of some 14–26 million people from famine-related illness and starvation occurred.
Prime agricultural land in the United States is being replaced with
A) military bases. B) urban land uses. C) nature preserves. D) oil drilling. E) grazing land use.
____ ecosystems seem to be particularly sensitive to changes in acidity
a. Freshwater b. Marine c. Forest d. Grassland e. Alpine