题目

王飞同学练习拉单杠时，两臂平行握住单杠，在他两臂逐渐分开的过程中，手臂的拉力( ) A.逐渐变大                        B.逐渐变小C.先变小，后变大               D.先变大，后变小 答案：解析：设每个手臂的拉力为F，两个手臂的夹角为2θ，由题意可知2Fcosθ=mg，在两个手臂逐渐分开的过程中，θ角在逐渐增大，则cosθ值在逐渐减小，而mg不变，所以拉力F在逐渐增大，本题考查了力的合成与分解的知识.答案：AGetting rid of dirt, in the opinion of most people, is a good thing. However, there is nothing fixed about attitudes to dirt. In the early 16th century, people thought that dirt on the skin was a means to block out disease, as medical opinion had it that washing off dirt with hot water could open up the skin and let ills in. A particular danger was thought to lie in public baths. By 1538, the French king had closed the bath houses in his kingdom. So did the king of England in 1546. Thus began a long time when the rich and the poor in Europe lived with dirt in a friendly way. Henry IV, King of France, was famously dirty. Upon learning that a nobleman had taken a bath, the king ordered that, to avoid the attack of disease, the nobleman should not go out. Though the belief in the merit of dirt was long-lived, dirt has no longer been regarded as a nice neighbor ever since the 18th century. Scientifically speaking, cleaning away dirt is good to health. Clean water supply and hand washing are practical means of preventing disease. Yet, it seems that standards of cleanliness have moved beyond science since World War Ⅱ. Advertisements repeatedly sell the idea; clothes need to be whiter than white, cloths ever softer, surfaces to shine. Has the hate for dirt, however, gone too far? Attitudes to dirt still differ hugely nowadays. Many first-time parents nervously try to warn their children off touching dirt, which might be responsible for the spread of disease. On the contrary, Mary Ruebush, an American immunologist(免疫学家)，encourages children to play in the dirt to build up a strong immune system. And the latter position is gaining some ground. 1. The kings of France and England in the 16th century closed bath houses because        . A. they lived healthily in a dirty environment. B. they thought bath houses were to dirty to stay in C. they believed disease could be spread in public baths D. they considered bathing as the cause of skin disease 2. Which of the following best describes Henry IV’s attitude to bathing? A. Afraid.                      B. Curious. C. Approving.                   D. Uninterested. 3.How does the passage mainly develop? A. By providing examples. B. By making comparisons. C. By following the order of time. D. By following the order of importance. 4.What is the author’s purpose in writing the passage? A. To stress the role of dirt. B. To introduce the history of dirt. C. To call attention to the danger of dirt. D. To present the change of views on dirt.