大家都着重在他是名词或复合形容词,可是对我来说,重点是标准格式单位的缩写,本来复数就不加s 顺手查了几个ref
https://goo.gl/P1g1QD "The letter "s" is never added toa symbol to indicate a plural. In other words, 2 minutesis written 2 min, not 2 min. or 2 mins."
https://goo.gl/QiiTJy "There is no need to add an s toan abbreviation to show a plural"例如长度也是 5 cm, 3 mi, 小时也是 3 h 而不是 3 hsBBC那个只是刚好他也是复合形容词的一部份所以本来就单数型