2020届二轮复习 概要写作专练(含答案) 学案

高三概要写作专练

tent. A new study suggests that a couple days of camping in the great outdoors can reset your circadian clock and help you get more sleep.

2 The circadian clock, more commonly known as the body clock, is an internal system that tells our bodies when it’s time to go to sleep and when it’s time to wake up. Scientists track this clock by measuring the amount of melatonin circulating in a person’s bl ood at any given time. In a healthy sleeper, melatonin levels rise a few hours before bedtime, stay high through the night, and then settle back down when it’s time to wake up.

3 In our modern society, however, most of us stay up many hours past sunset and would probably sleep in many hours after sunrise if we could. And the trouble is, your melatonin levels may still be high when your alarm clock goes off in the morning, which leads to grogginess. It may also have other health consequences as well, such as diabetes, overweight and heart disease.

4 Professor Kenneth Wright of the University of Colorado in the US wanted to see if our body clocks can be reset by a short stay in nature. His team recruited 14 physically active volunteers in their 20s and 30s. Nine went on a weekend camping trip, while the other five stayed home. At the end of the weekend, the researchers reported that in just two days, the campers’ body clock had shifted so that their melatonin levels began to rise more than an hour earlier than they did before they left on the trip. By contrast, the body clocks of the group that stayed home shifted even later over the course of the weekend. “This tells us we can reset our clocks fast,” Wright said.

5 Therefore, if you want to change your sleep patterns you could try to increase your exposure to natural light during the day and decrease the amount of artificial light you see at night.

get bigger. Right now, a little more than 7.3 billion people share the planet. By 2050, some scientists estimate, the world’s population may reach 9 billion. However, the changing climate will probably make feeding this far greater number a very frightening task. That is the conclusion reached by some scientists.

2 Just three crops—wheat, rice and corn—provide more than two-thirds of the calories that people consume. Such crops, and a small number of other important crops, come from farming regions someti mes referred to as “breadbaskets”. However, these areas often occupy a relatively small portion(部分) of the globe. Worse still, the breadbaskets are easily affected by bad weather. Events such as widespread flooding or extended heat wave can kill crops. Tha t’s especially true if the bad weather occurs when a crop is young, fruiting or approaching harvest.

3 Unfortunately, big crop failures in two or more breadbaskets could lead to what researchers call a “food shock”. That means an overall shortage of food would occur. Extreme food shocks used to happen every century. Or to put it another way, that’s only about once in very four generations of humans. However, according to studies, as the climate warms, high and low temperatures become more extreme, and by 2050, food shocks could occur about once every 30 years. In other words, a person born in the middle of the current century might live through two or three extreme food shocks during their lifetime.

4 So what can people do to help avoid food shocks? Making agriculture efficient is one choice. But one of the most effective ways to fight against food shocks might be to cut down on food waste. “If we could cut food waste in half,” said Seth Cook, a British environmental scientist, “we could feed an extra billion people.”