本文可以从“公众号菜单->英语知识-英语其他->英语习题”找到。must 和 have to 两者都表示“必须”，但 must 侧重于说话者的主观看法，认为有必要或有义务去做某事；have to 则重于客观需要，含有“不得不”或 “被迫”之意。 一、在做此类题目时，可以按以下顺序的判断规则来选择正确的用词。1、通过句中是否有其他情态动词或者来决定用 must 还是 have to，若句中有情态动词如 will 或 may 等，则就用 have to.2、若句中没有情态动词，则就判断是否要用否定形式，因为它们的否定形式意义完全不一样，must 的否定式 mustn’t 意为“一定不要”、“不允许”；而 have to 的否定式 don’t have to 意为“不必”。3、最后就根据句意判断是说话者的主观看法，还是客观需要；主观“义务”用 must，客观“义务”通常用 have to.
二、用 must 或 have to 及其过去式或它们的否定式来完成下面的句子，个别可能有多个答案1. If you are over 18 in California, you ____ take a driver training course to get a driver's license. You can have a friend or a family member teach you instead. But remember, you ____ still get your permit before you start practicing.2. You ____ be rich to be a success. Some of the most successful people I know haven't got a penny to their name.3. My car broke down in Death Valley last week. I ____ have it towed more than a hundred miles to the nearest mechanic.Lilly: That ____ have cost a fortune!4. While hiking in Alaska, you ____ keep an eye out for bears. If you see one, you ____ approach it. They are beautiful animals; however, they are wild and unpredictable in nature. You ____ be afraid of them, but educating yourself about the dangers can help keep you safe.5. I ____ go to work tomorrow because it is Memorial Day. The best thing about a day off from work is that I ____ get up at 6:00; I can sleep in till noon if I want to.三、答案、参考翻译及解析 1. don't have to，must如果你在加州年满18岁，你不必参加驾驶培训课程就可以拿到驾照。你可以让朋友或家人来教你。但请记住，在你开始练习之前，你还必须拿到许可证。解析：从 instead 且句意可以看出，前面要用一般式的否定 don't have to；后半句用 must，因为副词 still 置于实义动词之前，情态动词之后。2. don't have to你不一定要有钱才能成功。我认识的一些最成功的人都身无分文。解析：根据句意用 don't have to.3. had to，must我的车上周在死亡谷抛锚了。我不得不把它拖了一百多英里到最近的修理工那里。莉莉：那一定花了不少钱！解析：根据句意拖一百多英里是客观需要及 towed，所以前面用 had to；must have done 表示对过去的行为或动作进行推测，have to 没有表推测的用法。4. must，mustn't，don't have to在阿拉斯加徒步旅行时，你必须留意熊。如果你看到一个，你不能靠近它。它们是美丽的动物；然而，它们是野生的，本性难以捉摸。你不必害怕他们，但教育自己的危险可以帮助你的安全。解析：留不留意是说话者的主观看法，所以用 must；根据句意第二三空用 mustn't，don't have to.5. don't have to，don't have to我明天不用上班，因为今天是阵亡将士纪念日。休息一天最好的事情是我不必在6点起床；如果我愿意，我可以睡到中午。解析：根据句意两者都用 don't have to 而不用 mustn't，因为 mustn't 表示禁止做某事，不符合题意。
