英语中很多词可以同时具有两个或两个以上的词性，各词性之间的意思有的有些关联也有的毫无关联。例如cement作名词用是“水泥”的意思，而在It’s difficult to cement a good working relationship between employers and employees.这个句子中，cement作动词用是“连接，巩固”的意思。再如，content这个词有三个词性，分别是名词，形容词和动词，作不同词性时意思也不尽相同。所以在复习单词时要注意单词词性的变化及其相应的词义。

　　adolescent

　　n.(尤指16岁以下的)青少年

　　In retrospect, I was much happier as an adolescent with simple and vague dreams.

　　现在回想起来，青少年时的我要快乐得多，那时候我有着单纯、朦胧的梦想。

　　As diet and health improved, children and adolescents have, on average, increased in height by about an inch and a half every 20 years, a pattern known as the secular trend in height.(考研真题)随着饮食和健康的改善，每过20年儿童和青少年的身高会平均增长大约1.5英寸，这就是我们所知的身高增长的长期趋势模式。

　　adj.青春期的

　　【派生】adolescence n.青春期

　　advocate

　　v.提倡, 鼓吹

　　Nothing could persuade me to return to the kind of life Kelsey used to advocate and I once enjoyed. (考研真题) 没有什么能说服我再回到那种凯瑟过去提倡而我也曾经喜欢的生活模式中去。

　　n.拥护者，鼓吹者

　　【点睛】经过观察，学生对advocate作名词“拥护者”的意思更为生疏，而且在英语写作中也很需要这个词，所以请注意下面例句中的用法。

　　Scientists need to respond forcefully to animal rights advocates, whose arguments are confusing the public and thereby threatening advances in health knowledge and care.(考研真题)科学家应强有力的回应动物权利鼓吹者，因为他们的言论混淆了公众的视听，从而威胁了健康保健知识的发展。

　　ally

　　['?lai] n.同盟者

　　France is a traditional ally of the United States, with a shared history going back to the American Revolution.

　　【点睛】这个词作名词和作动词时的发音不一样。另外，在作动词时常与介词to或with搭配使用。

　　[?'lai] v.使结盟，使联姻

　　They have never sought to ally themselves to the local authorities. 他们从未设法与地方权力机构结成联盟。

　　【派生】

　　alliance n.结盟

　　The seven countries entered into an economic alliance to jointly (共同的) combat the global financial storm.

　　allied adj.结盟的

　　The allied army was so vast that the space it took up while camped was equivalent to a three-day march.盟军的军队太多了，他们的营地绵延的距离可以走上三天。

　　alternate

　　v.轮流

　　The new parents alternate turns changing the baby’s diapers, first the father changes the diapers, then the mother does.初为人父母的家长轮流给婴儿换尿布，爸爸先换，然后妈妈换。

　　adj.交替的

　　True innovators search for alternate methods, which may prove easier and more efficient

　　【派生】

　　alternation n.交替

　　The alternation between summer and winter is new to me because I grew up in the tropics.

　　alternative n.可供选择的东西

　　Both of the alternatives may cause me to regret my decision. 这两个可供选择的东西都会使我后悔自己的决定。

　　adj.两者挑一的

　　For safety’s sake the Emperor’s bodyguards chose an alternative route.为安全起见，君主的保镖选了另一条路线。

　　【点睛】这个词让许多学生感到困惑，alternative表示“两者或两者以上可以择一的，可以从数个中任择一个的”，如：I chose yoga from those alternative ways of coping with stress. 这句话表示，有很多种可供选择的减轻压力的方式，瑜伽是其中之一，我选择了瑜伽。alternative还可以表示“替代性的，非正统的，非主流的”，如：In that region wind power grows as alternative energy source. 我们知道，较之传统使用的煤、天然气的能量，风能、太阳能是非传统的，可作为替代性的能源。这句话就表示，“在那个地区，风能已成为替代性能源。”讲到alternative, 必然要讲下面这个词alternatively。

　　alternatively

　　adv.二者选一地，或者

　　Alternatively, if the star is relatively small, any life-supporting planets would have to adhere to a close orbit. 换句话说，如果恒星相对较小，那么能让生命存活的行星就必须在挨着离着很近的轨道。

　　【点睛】在上面这句话里alternatively的意思是“或者说，换个说法，换句话说”。再看下面例句：We could go to the park, or alternatively go to the aquarium. 这句话表示可以去公园，也可以去水族馆，哪个地方都行。

　　approach

　　v. 1.靠近 They heard footsteps approaching the door.

　　2.找…商量 Did she approach her mother for advice?

　　3.(着手)处理 (deal with) We should approach this problem in a creative way.

　　Researchers in the late 1960 covered that humans are born with the capacity to approach challenges in four primary ways: analytically, procedurally, relationally (or collaboratively) and innovatively.(考研真题)六十年代末研究者称人类与生俱来能用四种主要方法应对挑战，即深入分析、有序进行、协调合作，创造革新。

　　n. 1.接近 The cat’s approach frightened the chickens away.

　　2.方法

　　This approach, originated abroad, offered inventors medals, cash prizes and other incentives.这种源自国外的方法给发明者提供了奖章，现金奖励和其它激励机制。

　　According to many books and articles, New England’s leaders established the basic themes and preoccupations of an unfolding, dominant Puritan tradition in American intellectual life. To take this approach to the New Englanders normally mean to start with the Puritans’ theological innovations and their distinctive ideas about the church-important subjects that we may not neglect.(考研真题)根据很多书籍和文章所述新英格兰的领导阶层把演变的、占主流的清教徒传统作为美国精神生活的基本主题和主要关注点。用这种方法认识新英格兰人通常意味着要从清教徒的神学创新开始，还有他们对于教派重要性这个主题与众不同的看法也不容我们忽视。

　　【派生】approachable adj.可接近的，平易近人的

　　approximate

　　v.接近，约等于

　　If X equals 5.2, the value of Y approximates 3.7.

　　adj.大约的

　　Laureen had brought boxes full of sneakers with bright colors and psychedelic designs, which she then distributed to the barefoot children according to their approximate sizes. 劳琳带来几个箱子，里面装满了色彩艳丽的运动鞋，她按着脚的大致尺寸把鞋子发给了光着脚的孩子们。

　　【派生】

　　approximately adv.近似

　　During several years of gambling in that casino, Williams, a state auditor earning $35,000 a year, lost approximately $175,000.(考研真题)在那个赌场赌博的几年间，威廉姆斯，这位每年挣三万五千美元的州审计员输了大约十七万五千美元。

　　approximation n.近似值

　　Mathematicians will judge our equation to be an acceptable approximation even if it is not an exact equivalence. 即使等式不完全对等，数学家们也会认为我们的等式是一个可以接受的近似值。

　　auxiliary

　　adj.辅助的

　　Basic computer skills should be included as an auxiliary course in school.(考研真题)基础计算机技能应该成为学校的辅修课程。

　　n. 1.助手，帮手;辅助物 Nursing auxiliaries are assigned to several hospitals.

　　Your remarks in the court were necessary auxiliaries to my brother’s acquittal.你法庭上的陈词是宣判我哥哥无罪必不可少的辅助陈述。

　　2.助动词(auxiliary verb)

　　average

　　n.平均，平均数

　　【搭配】on average 平均

　　On average, women live longer than men.

　　v.求平均数，平均起来

　　【点睛】average的三个词性中，动词词性是学生所不熟悉的，学生总以为这个词不能直接用作动词，其实是可以的。

　　When we average the scores of our class we find that our class average is significantly higher than the school average.算完我们班的平均成绩，发现我们班的平均成绩高于学校平均成绩。

　　adj.平均的

　　According to the Centers for Disease Control and Prevention, average height—5′9′′ for men, 5′4′′ for women—hasn't really changed since 1960.(考研真题)根据疾病控制预防中心数据，男性平均身高5′9′′，女性平均身高5′4′′，这个数值从1960年以来没有太大改变。