passage 67 人类农业活动产生的气候变暖要追溯到更早

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看题，确定解题和阅读策略：

1. Which of the following best describes the function of the highlighted sentence? 句子功能

2. The author mentions “natural trends” most likely in order to  信息目的

这两题都是结构题，更多考察信息关系，阅读过程中可以弱化内容。理想状态下，可以只看局部信息关系来解题。

文章讲解：

①Scientific consensus is that humans first began to have a warming effect on Earth’s climate within the past century, after coal-burning factories, power plants, and motor vehicles began releasing carbon dioxide (CO2) and other greenhouse gases in significant quantities into the air. ②However, evidence suggests that human agricultural activities may have had such an effect much earlier: concentrations of CO2 started rising about 8000 years ago, even though natural trends indicate they should have been dropping; methane levels rose similarly about 3,000 years later. ③Without these rises, however, current temperatures in northern parts of North America and Europe would be cooler by three to four degrees Celsius—enough to inhibit agriculture—and an ice age would probably have begun several thousand years ago in northeastern Canada.

1. Which of the following best describes the function of the highlighted sentence?句子功能

A. It undermines the assumption that human activity has had a significant impact on Earth’s climate 常错干扰选项。没有证据/相反，比较点不是影响，而是时间

B. It supports the assumption that Earth’s temperatures have risen appreciably over the past 100 years 句子属性相反/没有证据

C. It questions the assumption that greenhouse gases have had a warming effect on Earth’s climate 没有证据，不是讨论“有没有”，而是在说“早晚”，所以缺少时间维度，同A

D. It challenges the assumption that human activity began to affect Earth’s climate after the advent of industrialization 关注同义替换

E. It supports the assumption that greenhouse gases are a directby-product of industrial activities 句子属性相反/没有证据

2. The author mentions “natural trends” most likely in order to 信息目的

A. propose a possible explanation for why current temperatures in North America and Europe are not as low as they might otherwise be 相反/无关

B. explain why levels of methane in Earth’s atmosphere began to rise approximately 5,000 years ago 没有证据/无关

C. suggest that Earth’s climate would have become even warmer without the advent of human agricultural activities 没有证据/无关/相反

D. identify factors that may have contributed to the rise of greenhousegases in Earth’s atmosphere approximately 8,000 years ago and again some 3,000 years later 无关/没有证据/相反

E. support the claim that human activity may have played a role in the rise in CO2 and methane levels in the atmosphere thousands of years ago