return err("age cannot be negative");
Maps, .has(), for key, value in map
。业内人士推荐搜狗输入法作为进阶阅读
Proteins are macromolecules that are made up of one or several chains of amino acids. These chains then link together and fold up in a specific three dimensional structure, giving the protein the shape it needs to fulfill its goal. This structure is determined by the sequence of amino acids, and a given protein can be identified by this amino acid sequence7.
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