could 和 might 都可用于表示可能性，而且 might 表示的可能性较小。couldn't 表示事情不可能发生，有较强的事实迹象，而 might not 用来表示事情有可能不发生，基本上就是凭空想象，所以要选用哪个，要根据上下文来判断；could 还是 can 的过去式，所以 couldn't 还可以表示过去没能力做某事。一、用 couldn't 或 might not 完成下面的句子 1. Unfortunately, James and Michelle had already made plans, so they _____ come with us to the exhibition at the Museum of Contemporary Art.2. They have had several major snow storms in the mountains during the last month. We had better call the highway patrol to check road conditions. The road to Smithsville _____ be passable.3. We should call Tim before we go over to his house; he _____ be there. I don't want to drive all the way there for nothing.4. In order to win the pie eating contest, Norman would have to eat sixteen pies in ten minutes. He _____ possibly eat that many pies - he would explode!5. I know Eve wants to go to the ballet with us, but we'd better call her before we get her ticket. She works Wednesday nights, and she _____ be able to get time off that evening.6. Susan _____ hear the speaker because the crowd was cheering so loudly.7. It _____ be a bad idea to take some snacks along while we're hiking. Last time, we got so hungry we had to come back early without finishing the hike.8. Jerry might be angry, or he _____. You never really know with him because he's so temperamental.9. Jerry _____ be angry at me. I've never done anything to upset him.10. The lamp _____ be broken. Maybe the light bulb just burned out.
二、答案、参考翻译及解析1. couldn't不幸的是，詹姆斯和米歇尔已经有了计划，所以他们不能和我们一起去当代艺术博物馆的展览。解析：根据句意判断应该用 couldn't，表示过去没办法做某事。2. might not 在过去的一个月里，他们在山区遇到了几次大的暴风雪。我们最好叫公路巡逻队检查路况。去史密斯维尔的路可能无法通行。解析：从 check the road conditions 还没发生可以看出，去史密斯维尔的路无法通行只是一种可能性。3. might not我们应该在去蒂姆家之前给他打个电话，他可能不在。我不想白白开车到那里去。解析：从 go over to his house 还没发生可以看出，蒂姆不在家只是一种可能性。4. couldn't为了赢得吃馅饼比赛，诺曼必须在十分钟内吃十六个馅饼。他不可能吃那么多馅饼-他会爆炸的！解析：从 explode 可以看出，在十分钟内吃十六个馅饼是不可能的事（即使能，也会撑坏的）。其实句子中的其他成分，都是用来衬托事情不可能发生，所以用 couldn't.5. might not我知道伊芙想和我们一起去看芭蕾舞，但我们最好在买票之前给她打电话。她星期三晚上上班，那天晚上可能不能请假。解析：不能请假只是一种可能性，所以用 might not.6. couldn't苏珊听不见演讲者讲话，因为人群欢呼声太大了。解析：表示过去不能做某事用 couldn't.7. might not当我们徒步旅行的时候带些零食可能不是个坏主意。上一次，我们太饿了，没走完就得早点回来。解析：不是个坏主意只是一种可能性，所以用 might not.8. might not杰瑞可能生气，也可能不生气。你永远不会真正了解他，因为他脾气很坏。解析：从前面的 might 及连词 or 可以看出，后面用 might not，因为 might 已经在表示可能性了。9. couldn't 杰瑞不可能生我的气。我从没做过让他不高兴的事。解析：根据后半句判断应该用 couldn't，因为如果用 might not，那么后面那句话一点作用都没有。10. might not这盏灯可能没坏。可能是灯泡烧坏了。解析：灯不亮，有可能是灯或灯泡的问题，也可能是其他的问题，比如停电，所以都是在表达一种可能性。
