What have humans done to maintain high crop yields?
A. They have developed synthetic versions of nutrients to help crops grow.
B. They have learned how to extract phosphorus from the air.
C. They have made synthetic inorganic fertilizers out of crude oil.
D. They have generated enough organic fertilizer to feed all the crops.
Answer: A
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262 Immigration to the United States steadily rose from 1800 to the start of the Civil War. The overwhelming number of immigrants who arrived before the Civil War were from Northern Europe (England, Germany and Ireland . Following the hiatus of the Civil War, immigration rose to its zenith in the period between 1880 and 1910, with immigrants from Southern and Eastern Europe (Italy, Greece,
Poland, Russia comprising the majority of new arrivals. The period between WWI and WWII saw an almost complete halt of immigrants to the United States. Immigration since the 1950s has markedly changed, with the majority of new arrivals coming from Latin America, Asia and Africa. What will be an ideal response?
Which of the following physical properties would you expect for krypton (Kr)?
A) a gas at room temperature B) hard C) brittle D) shiny E) conducts electricity
?There are four major types of terrestrial ecosystems called biomes.
Answer the following statement true (T) or false (F)
Most of the tall grass prairie of North America has been converted to ________
A) tundra B) savannas C) desert D) farmland E) tropical rain forest