Question

The pen bought by her is made in China. 为什么bought by her 做 the pen 的定

The pen bought by her is made in China. 为什么bought by her 做 the pen 的定语而不是主语补足语呢

Answer 1

bought是过去分词做后置定语，表示被动和完成。相当于定语从句which was bought by her
没有主语补足语这种说法。只听说过宾语补足语。

Answer 2

你先要知道主语补足语的概念

主语补足语就是在被动语态中，将宾语充当补充主语的作用。
例如 The boy was caught stealing.
steal的动作发生者是Boy 这才叫主语补足语 而这道题 buy的动作发生者是her 不是pen 怎么能是主语补足语呢

Answer 3

The pen(which is)bought by her is made in china.
省略了定语从句的部分，这个是用来描述这支笔的。整个句子的句干是：
The pen（主) is made(谓） in china（状）----被动句