为什么有时候可以省略介词?有这样一句话：A 12-year-old black boy,I attended a school there that was otherwise all white.之前A 12-year-old black boy是不是省略了介词as。但是如果改成：As a 12-year-old black boy,I attended a school there that was otherwise all white.又会感觉在逻辑上有问题，这个as用得不恰当。可以说一下原句的用法吗？
问题描述：
为什么有时候可以省略介词?
有这样一句话：A 12-year-old black boy,I attended a school there that was otherwise all white.之前A 12-year-old black boy是不是省略了介词as。但是如果改成：As a 12-year-old black boy,I attended a school there that was otherwise all white.又会感觉在逻辑上有问题，这个as用得不恰当。可以说一下原句的用法吗？
答
a 12-year-old boy 是主语的同位语
答
这个是英译汉常用的方法和技巧中的省略法，可以从修辞角度和汉语习惯来看。
答
a 12-year-old boy 是做状语,即being a 12-year-old boy,等于when I was 12 years old.