a(an)
n. a metric unit of length equal to one ten billionth of a meter (or 0.0001 micron); used to specify wavelengths of electromagnetic radiation 同义词：angstromangstrom unit
any of several fat-soluble vitamins essential for normal vision; prevents night blindness or inflammation or dryness of the eyes 同义词：vitamin Aantiophthalmic factoraxerophthol
one of the four nucleotides used in building DNA; all four nucleotides have a common phosphate group and a sugar (ribose) 同义词：deoxyadenosine monophosphate
(biochemistry) purine base found in DNA and RNA; pairs with thymine in DNA and with uracil in RNA 同义词：adenine
the basic unit of electric current adopted under the Systeme International d'Unites"a typical household circuit carries 15 to 50 amps"
同义词：ampereamp
the 1st letter of the Roman alphabet 同义词：letter a
the blood group whose red cells carry the A antigen 同义词：type Agroup A