[Casiopea]

I'll get to your questions in just a moment. First, though, I'd like to provide a bit on the function and distribution of complements.

There are two kinds of subject complements: adjective complements and noun complements.

Adjective complements, also called predicate adjectives, describe the subject, like this:

Mount Fiji is beautiful.
The window is broken.
The sky is blue.

Noun complements, also called predicate nominatives, rename the subject , like this:

She is a doctor. Note, 'a doctor' is a noun phrase.
John is my brother. Note, 'my brother is a noun phrase.
They are writers.

Subject complements follow linking verbs, whereas object complements follow objects. Subjects and objects tend to be nouns. That's why the words that modify subjects and nouns, or rather complete them, tend to be either nouns or adjectives. Other forms such as prepositional phrases and adverbs can in fact modify subjects and objects, but their function is that of a noun or adjective.

There are two kinds of object complements: adjective complements and noun complements. They follow the object. They describe or rename the object.

SVOC Adjective complement
Jackson got the reporters (O) excited (C).

('excited', a past participle, describes 'the reporters', the object, and so its functions is that of an object complement.)

SVOC Noun complement
They elected her (O) President (C).

('President', a noun, renames 'her', the object, and so its function is that of an object complement.)


SVOC can be paraphrased by a SVC structure, like this:

SVOC: They (S) elected (V) her (O) President (C).
SVC: She (S) is President (C).

Complements agree in number (singular/plural) with the words they complete (modify), like this:

They made her (O) a doctor (C).
==> Both 'her' and 'a doctor' are singular in number.

They made them (O) doctors (C).
==> Both 'them' and 'doctors' are plural in number.

:D