a
indefinite article The form a is used before consonant sounds and the form an before vowel sounds. When saying abbreviations like ‘FM’ or ‘UN’, use a or an according to how the first letter is said. For example, F is a consonant, but begins with the sound /e/ and so you say: an FM radio . U is a vowel but begins with /j/ and so you say: a UN declaration .-
used before countable or singular nouns referring to people or things that have not already been mentioned （用於可數名詞或單數名詞前，表示未曾提到的）一（人、事、物） -
used to show that somebody/something is a member of a group or profession （表示爲某一群體或職業中的一員） Their new car's a BMW. 他們的新轎車是輛寶馬。 She's a Buddhist. 她是佛教徒。 He's a teacher. 他是教師。 Is that a Monet (= a painting by Monet)? 那是莫奈的畫嗎？
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any; every 任何一；每一 -
used before uncountable nouns when these have an adjective in front of them, or phrase following them （用於前有形容詞或後有短語的不可數名詞前） a good knowledge of French 精通法語 a sadness that won’t go away 揮之不去的悲愁
used in front of two nouns that are seen as a single unit （用於視爲一體的兩個名詞之前） a knife and fork 一副刀叉
used instead of one before some numbers （用於某些數字前，代替 one） used when talking about prices, quantities and rates （用於價格、數量、比率等）一，每一 They cost 50p a kilo. 這些東西一公斤 50 便士。 I can type 50 words a minute. 我每分鐘能打 50 個單詞。 He was driving at 50 miles an hour. 當時他正以每小時 50 英裏的速度駕車。
a person like somebody 像（某人）的人；…式的人物 used before somebody’s name to show that the speaker does not know the person （用於某人姓名前，表示說話者不認識此人）有個 used before the names of days of the week to talk about one particular day （用於一星期中某天的名稱前，表示具體某一天）
Word OriginMiddle English: weak form of Old English ān ‘one’.