肯定句变否定句的技巧
一、动词后直接加not。

原句中含有be动词(am, is, are, was, were) 和助动词(have, has, had) 和情态动词(can, shall, will, may, should, would, might, had better 等)时，要在动词后直接加not。

如：
His mother has already called the police for help. (乌鲁木齐市中考题)
His mother ______ called the police for help ______. (答案：hasn’t, yet)
二、原句中没有be动词，助动词或情态动词时，要在行为动词前加助动词(do, does, did)与否定副词not的缩写形式。

另外，还需要将原句子中的some改为any；too改either；already改为yet。

还需要分清do, have等是实义动词还是助动词。

如(from )：
The old man hurt his leg last Wednesday. (西宁市中考题)
The old man ______ ______ his leg last Wednesday. (答案：didn’t hurt)
三、原句中含有every, everything, all, both等不定代词或both…and…, a lot of 等短语时，与否定副词not连用属部分否定。

把这些不定代词变成neither, none, no one或把both…and…变成neither…nor…时，才是全部否定。

如：
Both Joy and Sam like singing Beijing Oper a. (新疆中考题)
______ Joy ______ Sam likes singing Beijing Opera.(答案：Neither, nor)
四、在含有宾语从句的主从复合句中，当主句的主语是第一人称，谓语动词是think时，如果要否定后面的宾语从句，习惯上否定主句的谓语动词。

如：
I think she will come here soon. →I don’t think she will come here soon.。