(1) When a sentence is the structure of the main system, what part of speech is the word that modifies the predicate, is it an adverbial or an attribute?

Subject-predicate (verb)-predicate (component list)

In this sentence, the verb is a copula. Common copula verbs are: be (am, is, are, was, were), change: become, grow, turn, get (become), and sensory verbs: look, smell, listen, taste, feel, meaning "as if".

1. Mr Brown is an engineer. (noun as predicative)

Gradually he became silent. (Adjective as predicative)

She stood for an hour.

This problem has not been solved. (past participle as predicative)

This machine is out of order.

6. The TV is on. (Adverb as predicative)

His plan is to keep it a secret.

8. My job is to repair cars. (Gerund as predicative)

The question is what you want to do. A clause is a predicative, that is, a predicative clause.

Note: In the following sentences, adjectives are used as predicative, and infinitive structures are often followed by predicative.

I'm glad to meet you.

They are willing to help.

We are determined to follow his example.

Sentence 1. The predicative is the noun an engineer, and the adjective good can be added before it to modify the predicative. This adjective is the attribute that Mr. Brown is a good engineer.

The second sentence. Predicate is the adjective silent, which can be modified by adding an adverb very before it. This adverb can be used as an adverbial.

It depends on the specific situation, that is, what part of speech the predicative is.