美国人在打棒球时经常喜欢发曲线球，使球的方向会发生突变，这样给对方造成错觉，不能回击那个球。这和其他球类运动，如排球、乒乓球或网球，在发球时发转求的作用也很相似。逐渐地，这种让对方产生错觉，因而无法应付的球艺变成了日常用语：to throw a curve。
Curve就是曲线的意思。To throw a curve就是在打棒球时发曲线球。但是作为俗语，它的意思是给别人造成错觉，让他难以应付。请听一个刚刚考完历史的学生在埋怨他的教授：
例句-1: Professor Green certainly threw us a curve today. Half the questions were from parts of the book he told us to read but he never covered them in class. Of course, most of us didn't bother to read the stuff, so we really got caught.
这个学生说：格林教授今天可真是把我们难住了。考题的一半是他要我们看的那本书里的内容，可是他从来也没有在课堂上讲过。我们大多数人也都没有化时间去看那玩意儿，所以今天我们突然发现无法应付考题了。
To throw a curve还可以解释为“欺骗”。下面就是一个例子：
例句-2: My supervisor threw me a curve when he told me he would recommend me for the promotion. He didn't tell me he was also recommending three other people for the same job. So I didn't get it.
这个人说：我的上司欺骗了我，他告诉我他要建议给我提升。可是，他没有告诉我他同时还推荐了另外三个人担任同一个职位。结果我没有被提升。
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今天我们要讲的第二个俗语是：to throw for a loop。Loop是圆圈的意思。To throw for a loop是指“感到非常震惊”或者是“情绪很波动”。下面的例子是一个男朋友使得他的女朋友非常不高兴。这个女孩子说：
例句-3: Bill told me he couldn't take me out last night because he had to study for a big exam. So it threw me for a loop when I saw him walking into the movie theater with that stupid girl who sits next to him in biology class. (Recording defects: no audio for this part)
她说：比尔告诉我，他昨天晚上不能带我去玩，因为他要准备大考。所以，当我看到他和那个生物课坐在他旁边的傻姑娘一起走进电影院的时候我真是大吃一惊。
考试分数有时侯也会令人出乎意料的，请听下面的例子：
例句-4: When I saw my semester grade for the chemistry course, it really threw me for a loop! I was sure I'd get at least a "B"--but there it was in black and white: a "D". So I barely managed to pass.
这个学生说：“当我看到我的化学课学期成绩的时候，我真是吓了一跳。我满以为我至少能够得一个“B”，可是白纸上写的黑字是一个“D”。所以我刚刚及格。”