题目

关于自由落体运动，下列说法正确的是（    ）A.物体竖直向下的运动就是自由落体运动B.自由落体运动是初速度为零，加速度到为g的竖直向下的匀加速直线运动C.物体只在重力作用下从静止开始下落的运动叫自由落体运动D.当空气阻力的作用可以忽略不计时，物体自由下落的运动可视为自由落体运动  答案：BCD解析:根据对自由落体运动的正确理解可知，A错，B、C、D对. Why do men die earlier than women? The latest research makes it known that the reason could be that men’s hearts go into rapid decline when they reach middle age.The largest study of the effects of ageing on the heart has found that women’s longevity may be linked to the fact that their hearts do not lose their pumping power with age.“We have found that the power of the male heart falls by 20-25 percent between 18 and 70 years of age,” said the head of the study, David Goldspink of Liverpool John Moores University in the UK. “Within the heart there are millions of cells that enable it to beat. Between the age of 20 and 70, one-third of those cells die and are not replaced in men,” said Goldspink. “This is part of the ageing process.”What surprises scientists is that the female heart sees very little loss of these cells. A healthy 70-year-old woman’s heart could perform almost as well as a 20-year-old one’s.“This gender difference might just explain why women live longer than men,” said Goldspink. They studied more than 250 healthy men and women between the ages of 18 and 80, focusing on healthy persons to remove the confusing influence of disease.“The team has yet to find why ageing takes a greater loss on the male heart,” said Goldspink. The good news is that men can improve the health of their heart with regular exercise. Goldspink stressed that women also need regular exercise to prevent their leg muscles becoming smaller and weaker as they age.1.The underlined word “longevity” in the second paragraph probably refers to “________”.A. health B. long life C. ageing D. effect2.The text mainly talks about ________.A. men’s heart cells B. women’s ageing processC. the gender difference D. hearts and long life3.According to the text, the UK scientists have known that ________.A. women have more cells than men when they are bornB. women can replace the cells that enable the heart to beatC. the female heart loses few of the cells with ageD. women never lose their pumping power with age4.If you want to live longer, you should ________.A. enable your heart to beat much fasterB. find out the reason for ageingC. exercise regularly to keep your heart healthyD. prevent your cells from being lost5.We can know from the passage that ________.A. the rea son why ageing takes a greater loss on the male heart has been found outB. scientists are on the way to finding out why the male heart loses more o f the cellsC. the team has done something to prevent the male from suffering the greater lossD. women over 70 could lose more heart cells than those at the age of 20