材料一 让胡佛始料未及的是，这次“萧条”居然发展成世界性的经济危机！面对这场前所未有的危机，胡佛似乎显得不知所措，但还是采取了一系列的措施。其中包括： （1）设立周转基金用于资助农场主组建销售合作组织，确定最低销售价格。（2）成立谷类稳定公司，力图通过收购多余的粮食来制止价格的下滑。 （3）会见市长和州长，督促他们加速公共工程项目建设。 （4）设立国家信贷公司、紧急就业委员会，以期通过自愿联合来解决问题。 （5）支持通过减税议案，降低个人和私人企业的所得税。 （6）成立复兴金融公司，为银行、保险公司、农场抵押公司以及铁路公司提供贷款。 （7）建立住宅贷款银行，对有房产抵押的建筑与贷款公司、储备银行和保险公司给予贴现。 （8）扩大信贷资金，保证商业实体和个人享用更多的贷款。 ……

——摘编自［美［加里·纳什《美国人民：创建一个国家和一种社会》

材料二  美国在“新政”第一阶段，劳工的真正困难远未得到解决。1935年全国就业工人虽比1933年多了400万，但失业者仍达900万之多。从1933年起，工人依靠罢工手段，以进一步捍卫自己的切身利益。1934年，全美各地罢工持续不断，并以要求承认工会为主要目的。罢工打破了行业的界限，深入到过去很少发生罢工的诸如汽车工业、纺织工业等大批量生产的工业部门。

——吴于廑、齐世荣主编《世界史》

材料三 大萧条的一个重要标志是高失业率，但是罗斯福新政在这方面却收效甚微，1933年，罗斯福上台时的失业率是24．9%，至1940年失业率仍旧是14．6%（大萧条之前是3%左右），直到1941年美国全面卷入二战以后，失业率才下降到10%以下，并逐步达到大萧条前的水平。再看一下国防支出在战时经济中的巨额比重，1940年不过是17．9%，很快从1941年的46%跃升到1945年的89．5%，整个美国成为一个兵工厂，GDP自然增长了。至于失业率下降的一个更直接的原因是人们都参军去了，二战结束时美国军队有1200万人。

——彭斯达《美国经济周期研究：历史、趋势及中美经济周期的协动性》

如图所示，将一把钢尺紧按在桌面上，一端伸出桌面适当的长度，拨动钢尺，就可听到钢尺振动发出的声音.逐渐增加钢尺伸出桌面的长度，钢尺振动发出声音的音调会逐渐变____ .当钢尺伸出桌面超过一定长度时，虽然用同样的力拨动钢尺振动，却听不到声音，这是由于____ .

    Texting while walking is something that most of us are guilty of. We can't help replying to that message we just received. However, while it's fun to keep up with the latest gossip, we may actually be putting ourselves in danger.

    A team of researchers from two UK universities recently found that people who use their phones while on the move walk differently than usual.

    “Recently, a person in front of me was walking very slowly and weaving (迂回行进), and I thought, 'Is this person drunk?'” Matthew Timmis, co-author of the study, told the Guardian.

    It turned out that the person was just texting. Inspired by this, Timmis and his team set out to discover the effects of phone use on how we navigate streets.

    A group of 21 volunteers were asked to walk around a simulated (模拟的) street, complete with obstacles such as a step. The participants traveled the course a total of 12 times each, either writing or reading a message, making a call, or with no phone at all.

    It took the volunteers 118 percent longer to complete the course when using a phone. They also focused on the step obstacle 60 percent more and paid attention to the travel path 51 percent more when they weren't using a phone.

    Although there were no accidents, Timmis believes we should still be aware of what's going on around us.

    “The big risk here is suddenly-appearing hazards (危险), like a pedestrian (行人) suddenly walking in front of you,” he told the Guardian. “You are not going to be able to respond to that as efficiently, which increases the risk of injury.”

    To bring attention to the dangers of “text walking”, a temporary “texting lane” was set up in Antwerp, Belgium in 2015. And earlier this year, a special crosswalk featuring flashing red lights on the ground to get the attention of texters was set up in Wuhan, Hubei province.

    “Texting while walking can lead to collisions with poles or other pedestrians. You could even be endangering your own life when you cross the street without looking up,” a spokesperson for the company that made the Antwerp texting lane told Yahoo News.

当同学之间产生误会、矛盾或冲突时，会产生情绪的不满。这时我们要（    ）