在记忆和背诵考研英语单词时，我们一般推荐词根词缀法记忆法，这种方法科学合理，记忆牢固并且迅速，常用前缀、后缀可前往查看。词汇的前缀一般修饰或者改变单词的意思，词汇的后缀一般改变单词的词性。　　

1.dis-(加在名、形、动词前)表示“不，不再”

　　disadvantagen.不利，不利条件;

　　E.g. Depression is the third thing that works to my patients' disadvantage.

　　抑郁是威胁我的病人健康的第三大杀手。

　　disappear. v. 消失

　　E.g.He saw something dark disappear behind the curtain of leaves.

　　他看到一个黑漆漆的东西从浓密的树叶后消失了。

　　disconnect. v. 分离

　　E.g.You should disconnect the wireless set before you make adjustments inside it.

　　你应先拔掉无线电插头,再做内部调整。

2. di-,dif-, dis-：away，negative否定，分开，不

　　distrust. v. 不信任, 怀疑

　　E.g.What he saw there left him with a profound distrust of all political authority.

　　他在那儿的所见让他对一切政治当局产生了一种深深的不信任感。

　　disassemble v. 拆开

　　E.g.We had to completely disassemble the engine to find the problem.

　　我们只好把发动机全部拆开以寻找故障原因。

　　differentiate v.区分

　　E.g.A child may not differentiate between his imagination and the real world.

　　儿童可能无法将自己的幻想与真实世界区分开来。

　3. il-：(加在以“l”开头的词前)表示“不”

　　illiterate n. 文盲;

　　E.g.Many senior managers are technologically illiterate.

　　许多高级经理都对技术知之甚少。

　　illegitimate a. 非法的

　　E.g.The election was dismissed as illegitimate by the opposition.

　　反对党以不合法为由拒绝接受选举结果。

4. im-，in-(加在字母m，b，p之前)not，in，into否定，加强或引申意义

　　impracticable行不通的

　　E.g.Such measures would be highly impracticable and almost impossible to apply.

　　这样的措施非常不切实际,几乎不可能付诸实施。

　　invisible不可见的;

　　E.g.Parents fear they might overstep these invisible boundaries.

　　父母担心他们可能会逾越这些无形的界限。

　　irrational不合理的;

　　E.g. His behavior was becoming increasingly irrational.

　　他的行为变得越来越不理智了。

5. mal- bad，badly：恶，不良

　　maltreat虐待;

　　E.g.He said that he was not tortured or maltreated during his detention.

　　他说自己在押期间并未遭受拷问和虐待。

　　malnutrition营养不良

　　E.g.Infections are more likely in those suffering from malnutrition.

　　营养不良的人更有可能被传染。