a
01
一个
used when we want to talk about a person or thing for the first time or when other people may not know who or what they are
例子
She bought a new book yesterday.
她昨天买了一本新书。
She found a job at a company downtown.
她在市中心的一家公司找到了一份工作。
1.1
一个
used before a noun when we are not talking about a specific person or thing
例子
He has a problem that needs solving.
他有一个需要解决的问题。
She brought a gift for the birthday party.
她为生日派对带了一个礼物。
02
一个, 一名
used to show someone or something belongs to a group or type
例子
He is a member of a sports club.
他是体育俱乐部的一员。
He is a student in the university.
他是大学里的一名学生。
A
01
音高A, A音
the musical pitch A, which is a specific note in the diatonic scale commonly used in Western music
02
埃, 长度单位，等于一米的百亿分之一
a metric unit of length equal to one ten billionth of a meter (or 0.0001 micron); used to specify wavelengths of electromagnetic radiation
03
一个, 血型A
the blood group whose red cells carry the A antigen
04
罗马字母表的第一个字母, 字母A
the 1st letter of the Roman alphabet
05
腺嘌呤, 用于构建DNA的四种核苷酸之一
one of the four nucleotides used in building DNA; all four nucleotides have a common phosphate group and a sugar (ribose)
06
腺嘌呤, 存在于DNA和RNA中的嘌呤碱基
(biochemistry) purine base found in DNA and RNA; pairs with thymine in DNA and with uracil in RNA
