Today, there are a large number of ways to exercise and stay healthy. From working out in a gym to riding a bike to work, staying active may have never been easier. Despite all this, a new study finds Americans are actually much less active than their ancestors over 200 years ago. In fact, researchers from Harvard University say the average American people stay physically active for 30 fewer minutes than people did in 1820.

The team came to this conclusion after examining historical data which shows that body temperature among Americans has been falling for years. The results of a Stanford University report showed that the average body temperature of Americans has dropped from the age-old 98.6 degrees Fahrenheit(华氏温度)to about 97. 5 degrees.

They also looked at changes in metabolic rates(代谢率), which measure how physically active people are. Researchers found that the resting metabolic rate—the total number of calories the body burns while completely at rest—has declined by six percent since 1820. Researchers say metabolism plays a key role in producing body heat and much of this depends on how active a person is.

So what’s the cause of all this? “Instead of walking to work, we take cars or trains; instead of manual labor in factories, we use machines,” says lead author Andrew K. Yegian. “We’ve made technology do our physical activity for us. Our hope is that this helps people think more about the long-term changes of activity that have come with our changes in lifestyle and technology.”

The team also pulled data from two other studies to come up with an estimate of how much exercise Americans got in 1820 in comparison to today. “This will bring great benefits to my field of work because it can help us assess just how much increases in the incidence(发生率)of heart disease and Alzheimer’s is related to decreases in physical activity,” says Daniel E. Lieberman.

【小题1】What does paragraph 1 mainly tell us?

A．Americans’ way of working changes.

B．There are different ways to exercise.

C．Humans’ physical condition is getting worse.

D．Americans exercise less than people did before.

【小题2】Why does the author use two numbers in paragraph 2?

A．To provide an example.	B．To make a comparison.
C．To introduce a topic.	D．To describe a phenomenon.

【小题3】What mainly results in Americans exercising less?

A．The use of technology.	B．The health condition.
C．A change in metabolism.	D．A lack of time.

【小题4】What can we infer about Lieberman from the text?

A．He values physical exercise.

B．His job is related to medical field.

C．He is a patient with heart disease.

D．He will estimate American future technology.