Question

①当一个句子是主系表结构，那后面修饰表语的那个词的词性是什么，是做状语还是定语？

Answer 1

主语——谓语（动词）——表语(主系表)
这一句型中，动词是系动词，常见的系动词有：表示状态的动词：be (am, is, are, was, were),表示变化的动词：become, grow, turn, get(变得)，感官动词：look, smell, sound, taste, feel, 表示“似乎”的动词: seem, appear,表示持续的动词：keep, remain等，找出表语。
1.Mr.Brown is an engineer.(名词做表语)
2.Gradually he became silent.(形容词做表语)
3.She remained standing for a hour.(现在分词做表语)
4.The question remained unsolved.(过去分词做表语)
5.The machine is out of order.(介词短语做表语)
6.The television was on.(副词做表语)
7.His plan is to keep the affair secret.(动词不定式做表语)
8.My job is repairing cars.(动名词做表语)
9.The question is what you want to do.(从句做表语，即：表语从句)
注意：在下面的句子中，形容词做表语，在表语的后面常常接不定式结构。
I'm happy to meet you.
They are willing to help.
We are determined to follow his example.
句1.表语是名词 an engineer,其前可以加上一个形容词good修饰表语，这个形容词做定语Mr.Brown is a good engineer.
句2.表语是形容词 silent，其前可以加上一个副词very修饰表语，这个副词做状语Gradually he became very silent.
由上可知表语加什么词来修饰要看具体情况即：表语是什么词性

Answer 2

应该是副词，作状语。