an extraterrestrial
作可数名词，泛指一个外星人时用不定冠词 a/an。
In the story, an extraterrestrial lands in a small village.
故事里，一个外星人降落在一个小村庄。
源自地球大气层外、太空或另一颗行星的生物；外星人。；假定存在于地球或其大气层之外的生命形式
A living being that comes from outside Earth or its atmosphere, such as from another planet; an alien.
源自地球大气层外、太空或另一颗行星的生物；外星人。
A being originating from outside of the Earth's atmosphere, from space, or from another planet; an alien.
假定存在于地球或其大气层之外的生命形式
a form of life assumed to exist outside the Earth or its atmosphere
Scientists have not yet found any evidence of an extraterrestrial.
科学家尚未找到任何外星生物的证据。
用法提示：此处使用单数名词形式，指代未知的外星生命个体。
Many people believe that extraterrestrials have visited Earth.
许多人相信外星生物曾到访地球。
用法提示：此处使用复数形式，泛指外星生命。
The movie depicts a friendly extraterrestrial who helps humans.
这部电影描绘了一个帮助人类的友好外星生物。
用法提示：此处使用单数名词形式，指代具体的外星生命角色。
作可数名词，泛指一个外星人时用不定冠词 a/an。
In the story, an extraterrestrial lands in a small village.
故事里，一个外星人降落在一个小村庄。
特指上文提到或双方已知的外星人时用定冠词 the。
The extraterrestrial was taken to a secret laboratory.
那个外星人被带到了一个秘密实验室。
复数形式泛指外星人这一群体时，前面通常不加冠词。
Some people claim that extraterrestrials have visited Earth.
有些人声称外星人曾造访地球。
grammar · medium
易错句子The movie is about a extraterrestrial who lands in a small town.
正确表达The movie is about an extraterrestrial who lands in a small town.
extraterrestrial 以元音音素 /ɛ/ 开头，不定冠词要用 an，不能用 a；冠词的选择看的是读音的开头，不是拼写首字母。
grammar · medium
易错句子Two extraterrestrial were seen near the lake last night.
正确表达Two extraterrestrials were seen near the lake last night.
extraterrestrial 作可数名词，前面有具体数目时必须用复数形式 extraterrestrials；汉语名词没有数变化，容易漏加 -s。
grammar · medium
易错句子She says she once met extraterrestrial on her way home.
正确表达She says she once met an extraterrestrial on her way home.
extraterrestrial 是可数名词单数，指某一个外星人时需要加不定冠词 an 之类的限定词，不能像汉语“遇见外星人”那样光用名词本身。
alien 在科幻语境中与 extraterrestrial 同义，但更口语化、用途更广，还可指外国侨民；extraterrestrial 更正式，是科幻与学术文本中的术语，专指地球之外的生命形式。
两者拼写都以 extra- 开头、形态相近，但 extraterritorial 是法律用语，指不受所在国法律管辖的治外法权，与外星生命无关。
Martian 专指火星居民或火星来客，是 extraterrestrial 的一个具体类别，不能用来泛指来自任何星球的外星生命。
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