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。
