eighteen years old
作表语说明年龄,主语通常是人。
My sister is eighteen years old.
我妹妹十八岁。
在十七之后和十九之前的基数,罗马数字为XVIII,阿拉伯数字为18；十八个
the number 18; one more than seventeen and one less than nineteen
在十七之后和十九之前的基数,罗马数字为XVIII,阿拉伯数字为18
The cardinal number occurring after seventeen and before nineteen, represented in Roman numerals as XVIII and in Arabic numerals as 18.
There are eighteen students in our class.
我们班有十八名学生。
用法提示：“eighteen”为基数词，表示数量“十八”。
She turned eighteen last month.
她上个月满十八岁了。
用法提示：“eighteen”为基数词，此处表示年龄“十八岁”。
The book has eighteen chapters.
这本书有十八章。
用法提示：“eighteen”为基数词，修饰名词表示“十八”。
作表语说明年龄,主语通常是人。
My sister is eighteen years old.
我妹妹十八岁。
介词短语 at eighteen 指“在十八岁那年”,用于说明人生阶段。
She left home at eighteen.
她十八岁时离开了家。
表示整体中的十八个;of 后需接带 the、these、my 等限定词的名词或代词。
Eighteen of the thirty students passed the exam.
三十名学生中有十八人通过了考试。
直接放在复数可数名词前表示数量,名词用复数形式。
Eighteen people were waiting outside.
有十八个人在外面等着。
grammar · medium
易错句子My brother is eightteen years old.
正确表达My brother is eighteen years old.
eighteen 只写一个 t（eight + een）。thirteen、fourteen、fifteen 等是在基数词后加 -teen 构成的，容易让人误以为 eighteen 也要双写 t，但 eight 本身末尾已有 t，正确拼写是 eighteen。
grammar · medium
易错句子There are eighteen student in my class.
正确表达There are eighteen students in my class.
数词 eighteen 后面的可数名词必须用复数形式。汉语名词没有单复数变化，容易漏掉 -s；eighteen 表示不止一个，所以 student 要变成 students。
grammar · medium
易错句子This is my eighteen birthday.
正确表达This is my eighteenth birthday.
表示“第几个”要用序数词，所以是 eighteenth，不能用基数词 eighteen。汉语说“十八岁生日”时数字形式不变，容易直接搬用 eighteen；英语中 birthday 前表顺序必须用序数词 eighteenth。
十八岁
She is eighteen years old and about to start college.
她十八岁，即将上大学。
十八轮大卡车；重型卡车
An eighteen-wheeler blocked both lanes of the highway.
一辆十八轮大卡车堵住了高速公路的两条车道。
十八洞（标准高尔夫球场）
We played all eighteen holes before it got dark.
天黑前我们打完了全部十八个洞。
满十八岁
You can vote once you turn eighteen.
你满十八岁就可以投票了。
十八岁及以上
The club is open to anyone eighteen and over.
这家俱乐部对十八岁及以上的所有人开放。
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