相关Belowisaselectionfro的文学知识

问题详情：Belowisaselectionfromapopularsciencebook.Ifbloodisred，whyareveins(静脉)blue?Actually，veinsarenotblueataremoreofaclear，yellowishoughbloodlooksredwhenit'soutsidethebody，whenit'ssittinginaveinneart...