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People, like most animals, are naturally lazy. So the ascent of mankind is something of a mystery. Humans who make their livings hunting and gathering in the traditional way do not have to put much effort into it. Farmers who rely on rain to water their crops work significantly harder, and lead unhealthier lives. But the real back-breaking is that carried out by farmers who use irrigation. Yet it was the invention of irrigation, at first sight so harmful to its practitioners that actually produced a sufficient surplus to feed the priests, scholars, artists and so on whose activities are collectively thought of as "civilization".
In the past 10,000 years, the world’s climate has become temporarily colder and drier on several occasions. The first of these, known as the Younger Dryas, after a tundra-loving plant that thrived during it, occurred at the same time as the beginning of agriculture in northern Mesopotamia. It is widely believe
A. was accompanied by hardships of human existence.
B. is a mystery as yet unknown to mankind.
C. can be attributed to the innovative sparks of ancestors.
D. was recorded by history books ending at that time.
Most people think of zoos as safe places for animals, where struggles such as difficulty finding food and avoiding predators don’t exist. Without such problems, animals in zoos should live to a ripe old age.
But matter may not be true for the largest land animals on Earth. Scientists have known that elephants in zoos often suffer from poor health. They develop diseases, joint problems and behavior changes. Sometimes, they even become infertile or unable to have babies.
To learn more about how captivity affects elephants, a team of international scientists compared the life spans of female elephants born in zoos with female elephants living outdoors in their native lands. Zoos keep detailed records of all the animals in their care, documenting factors such as birth dates, illnesses, weight and death. These records made it possible for the researchers to analyze 40 years of
A. They do not like living in herds.
B. They do not get enough exercise.
C. They do not live with their families.
D. Both B and C.
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