题目内容：

The arm bones of women who lived 7-000 years ago show a surprising level of strength-even higher than today's professional athletes. That's according to a first-ever study comparing prehistoric(史前的)bones to those of living people. The finding suggests a revision of history — the everyday lives of prehistoric women were filled with hard labor, rather than just sitting at home doing lighter tasks while the men struggled and fought for life.

“Before the study, there are no clear records describing how our ancient ancestors lived. It can be easy to forget that bone is a living tissue, one that responds to the difficulties we put our bodies through,” said lead author Alison Macintosh. “Physical force and muscle activity both put pressure on the bone. The bone reacts by changing in shape, thickness and other aspects over time. ”

Previous studies only compared female bones to contemporary male bones, the researchers said — and that's a problem, because the response of male bones to stress and change is much bigger than that of women. For instance, as humans moved from a hunter-gatherer lifestyle constantly on the move to a more settled agrarian (农耕的)one, changes can be observed in the structure of the shinbone (胫骨) 一 and these changes were much more evident in men.

However, a comparison of the bones of prehistoric women to the bonos of living female athletes can help us work out a more accurate picture of what those prehistoric women were doing. “By analyzing the bones of living people and comparing them to the ancient hones, we can start to explain the kinds of labor our ancestors were performing,” Macintosh said. What they found was that women's leg strength hasn’t changed a great deal, but their arms used to be very powerful. Prehistoric women, the researchers found, had arm strength 11〜16 percent stronger than those of modern rowers, and 30 percent stronger than those of non-athletes.

1.What does the study tell about prehistoric women?

A. They were stronger than men.

B. They had lighter bones than men.

C. They did tough tasks as the men.

D. They spent most time staying at home.

2.What problem did previous studies on prehistoric bones have?

A. They lacked enough comparison.

B. They only studied men's bones.

C. They focused little on bones.

D. They ignored the lifestyles.

3.What does the underlined word “that” in Paragraph 3 refer to?

A. Bones’ structure.

B. Bones' thickness.

C. Bones’ response to stress.

D. Bones’ stress from hard labor.

4.What can we learn from the last paragraph?

A. It’s still hard to explain our ancestors' lifestyle.

B. Prehistoric women went through much suffering.

C. Women's arms have become much stronger over time.

D. Prehistoric women are stronger than contemporary females.