gmat语法，又叫句子改错(sentence correction)，是GMAT语文(VERBAL)三大题型中难度较高但也较容易提分的题型。因此，想要考好GMAT语法秒解难题还是需要花上一番功夫的。特别是对于考试涉及的各类语法点和疑难杂症，考生势必要多加努力才能有所收获。

GMAT考试中语法改错SC题型让考生比较头疼的一点在于考试本身覆盖的语法点太多，大家别考时间不够就很有可能出现遗漏或者来不及准备的情况。有鉴于此新航道小编建议大家从高频热门语法点开始优先准备起来。下面新航道小编就来分享must和have to的用法说明。

GMAT语法大百科语法点：must和have to的用法说明

1.must 助动词

must(必须)作<情态助动词>,相当于have to,但must强调主观因素,而强调客观因素。

I must go now. 我现在必须走。(我自己认为应该走了)

2.have to 助动词

(必须)是<情态助动词>,后接塬形<动词>,表示客观条件决定不得不做某事。

I have to go now. (我现在不得不走了)

GMAT高频词汇must和have to用法实例讲解

Although the manager agreed to a more flexible work schedule, he said that it must be posted on the bulletin board so that both management and labor will know what everyone is assigned to do.

(A) he said that it must be posted on the bulletin board so that both management and labor will know what everyone is

(B) he said it had to be posted on the bulletin board so that both management and labor knows what everyone is

(C) he said that they would have to post the assignments on the bulletin board so that management and labor knew what everyone was

(D) he said that the schedule would have to be posted on the bulletin board so that both management and labor would know what everyone was

(E) saying that the schedule had to be posted on the bulletin board so that both management and labor would know what everyone had been

选项分析：

首先，我们需了解这句话的语境，很显然这是一个类似于命令的要求的口吻。当发出命令或者指示的时候，must会比have to好得多。虽然有时候我们会用had to代替must做过去时态，但二者含义有差别。当需要精确表述的时候(如本题)，must不能用have to 取代。所以最后答案是A