a是虛詞還是實詞

實詞。

art. 一(個)每一(個)任一(個)

n. 英語字母表的第一個字母學業成績得優者表示“最好”的符號

例子

a metric unit of length equal to one ten billionth of a meter (or 0.0001 micron) used to specify wavelengths of electromagnetic radiation

any of several fat-soluble vitamins essential for normal vision prevents night blindness or inflammation or dryness of the eyes

one of the four nucleotides used in building DNA all four nucleotides have a common phosphate group and a sugar (ribose)

(biochemistry) purine base found in DNA and RNA pairs with thymine in DNA and with uracil in RNA