? ?I am under 13 years old. 此句中的under是介词。例如:? ? Children under six years old are admitted free. 未满6岁的儿童可免费入场。(摘自《英汉多功能词典》,外语教学与研究出版社出版发行,1997年1月第1版) ??? ? Nobody under 18 is allowed to buy alcohol. 未满18岁者不得买酒。(摘自《牛津高阶英汉双解词典》第9版 under prep.3)? ??? ? 下列例句中的 under 是副词(后面不能接数字)? ? children aged 12 and under?12岁及以下的儿童?(摘自《牛津高阶英汉双解词典》第9版?under?adv.3)? ? Children aged five and under [ = children who are five years old and younger] may enter the park for free. 五岁及五岁以下的儿童进公园免费。(摘自《韦氏高阶英汉双解词典》under?adv.2)