基数词和序数词的用法学习知识点精析精练
数词分两类:基数词和序数词。表示数目的词叫基数词，表示须序的词叫序数词。
数词主要分为基数词和序数词，先来看基数词的用法：
1. 基数词一般可写成如345或three hundred and forty-five.
2. 基数词一般是单数形式,但遇下列情况,常用复数:
（1）与of 短语连用,表示概数,不能与具体数目连用,如scores of people 指许多人;
（2）在一些表示"一排"或"一组"的词组里.例如:
They arrived in twos and threes. 他们三三两两的到了.
（3）表示"几十岁".
（4）表示"年代",用 in +the +数词复数.
（5）在乘法运算的一种表示法里,如Three fives is(are)fifteen.
序数词的用法：序数词的缩写形式如first---1st second---2nd thirty-first---31st等。
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1. 倍数表示法（1）主语+谓语+倍数(或分数)+ as + adj. + as.例如I have three times as many as you. 我有你三倍那么多.（2）主语+谓语+倍数(分数)+ the size (amount,length…) of….例如:The earth is 49 times the size of the moon. 地球是月球的49倍.（3）主语+谓语+倍数(分数)+ 形容词(副词)比较级+ than….例如:The grain output is 8 percent higher this year than that of last year. 今年比去年粮食产量增加8%.（4）还可以用by+倍数，表示增加多少倍。例如:The production of grain has been increased by four times this year. 今年粮食产 量增加了4倍.2. 分数表示法的构成：基数词代表分子，序数词代表分母。分子大于1时，分子的序数词用单数，分母序数词用复数。例如：1/3 one-third; 3/37 three and three-sevenths.The Science of Risk-SeekingSometimes we decide that a little unnecessary danger is worth it because when we weigh the risk and the reward, the risk seems worth tasking. 71 Some of us enjoy activities that would surprise and scare the rest of us. Why? Experts say it may have to do with how our brains work.The reason why any of us take any risks at all might have to do with early humans. Risk-takers were better at hunting, fighting, or exploring. 72 As the quality of risk-taking was passed from one generation to the next, humans ended up with a sense of adventure and a tolerance for risk.So why aren’t we all jumping out of airplanes then? Well, even 200,000 years ago, too much risk-taking could get one Killed. A few daring survived, though, along with a few stay-in-the-cave types. As a result, humans developed a range of character types that still exists today. So maybe you love car racing, or maybe you hate it. 73 No matter where you are on the risk-seeking range, scientists say that your willingness to take risks increases during your teenage years. 74 To help you do that, your brain increases your hunger for new experiences. New experiences often mean taking some risks, so your brain raises your tolerance for risk as well. 75 For the risk-seekers, a part of the brain related to pleasure becomes active, while for the rest of us, a part of the brain related to fear becomes active. As experts continue to study the science of risk-seeking, we’ll continue to hit the mountains, the waves or the shallow end of the pool.A. It all depends on your character.B. Those are the risks you should jump to take.C. Being better at those things meant a greater chance of survival.D. Thus, these well-equipped people survived because they were the fittest.E. This is when you start to move away from your family and into the bigger world.F. However, we are not all using the same reference standard to weigh risks and rewards.G. New brain research suggests our brains work differently when we face a nervous situation.
