But are they kidding themselves to think a walk is really helping them? Should we all be running or jogging if we want to count that activity as good for us? Dr. Tim Church, who studies the effects of physical activity at Louisiana State University's Pennington Biomedical Research Center, made a study about that.

　　Church headed a study with 464 postmenopausal (绝经后的) women who, for six months, came into the lab to walk a treadmill (跑步机) while researchers watched.

　　The first group walked for 73 minutes a week, the second 136 minutes a week and the third 190 minutes weekly. These women were walking slowly, and could easily carry on a conversation.

　　"Surprisingly, the group that was only walking for 73 minutes a week slowly benefited a lot，" Church says. They say they've gotten more physically active from walking. They haven't necessarily lost weight, but their pants fit differently.It's because they have less belly fat, he says, which is a very good thing. This document from the American Heart Association lists dozens of studies showing similar benefits from walking.

　　And in Church's study, participants gained more than physical benefits. They also gained benefits like less anxiety and fewer symptoms of depression: They also discovered something many of us long for: more energy.

　　"It wasn't a dose­response (剂量效应) - as in, 'the more exercise you did, the more your energy increased，'"Church says. "Actually, all three exercise groups increased their levels of energy the same."

语篇解读：本文是议论文。文章通过研究证明散步有益健康，并且运动量和强度与受益程度不成正比。

　　4．What does the underlined word "that" in Paragraph 2 refer to?

　　A．If people should walk the dog.

　　B．The effect of running or jogging.

　　C．If people need to exercise hard to benefit.

　　D．The importance of doing exercise regularly.

解析：选C　代词指代题。由第二段开头的"But are they kidding themselves ... as good for us？"及下文的研究可推断，画线词指代人们是否必须做高强度的