前缀di-,twi-分别来源于希腊语和古英语 twa。大家一定还记得拉丁前缀bi-吧，现在要介绍的di-是与bi-同义的希腊语源的前缀，它的意思也是twice,two。其实，di-与bi-在印欧语中是同源的。di-最早出现在希腊语源的借词中，只与希腊词根缀合。但在现代英语中，di-成为很有用的术语前缀，可以跟单词相结合，构成科技术语，尤其是化学术语。

1.dilemma
n. a situation which poses two or more difficult choices进退两难 *di (=tow),lemma (=proposition)
例句：If I go to the party,my parents will be angry,but if I don't go ,my boyfriend will get angry. Oh,what a dilenmma.如果我去参加聚会，我的父母会生气，但是如果我不去，我的男朋友会生气。唉，直是进退两难。

2.dioxide
n. a compound containing two atoms of oxygen二氧化物 *di (=two),ox (=acid,sharp)
例句：Plants can absorb carbon dioxide and release oxygen.植物能够吸收二氧化碳，释放氧气。

3.diphthong
sound made by joining two vowels 双元音 *di (=tow),phthong(=sound)
例句：English diphthongs are especially difficult to pronounce if you native language does not use them.如果你的母语中不存在双元音，你就会觉得英语的双元音发音很难。

4.diverge
v.get farther apart from a point or from each other as they progress;turn off,deviate分叉；分歧；脱离，背离 *di (=apart),verg(=lean)
例句：Over the years our interests diverge and we hardly even talked to each other.随着时间的流逝，我们之间的兴趣点产生了分歧，甚至彼此都不说话了。

5.divide
v. separate into parts 分开，分离
n. something that divides,especially a watershed 分开的东西，尤指分水岭 *di<dis(=apart),vid(=look)
例句：if we divide the work among us ,we'll get it done a lot quicker.如果我们分开来做这项工作，我们将完成得更快。

6.divorce
v. put an end to a marriage by law,separate （使）离婚；分离
n. legal ending of a marriage,ending of a connection or relationship离婚；断绝血缘关系 *vorc<vers(=turn)
例句：Some 40% of marriages in the U.S. end up in divorce.在美国，40%的婚姻是最终走向离婚。

7.twifold [twi- 二 + fold 折叠，倍]
adv.& adj. 两倍,双重

8.twiforked [twi- 二 + fork 叉 + -ed 后缀]
adj.有两叉的