Read the sentence.

With enough credits, I had become an astronomy major.

Which word or phrase is the subject complement in the sentence?

major

had become

credits

astronomy

The answer is A: major

Major

A subject compliment can be a noun. It can be a pronoun. Or, it can be an adjective if the adjective is describing the subject. Note it will immediately follow a linking verb. If we look at the sentence, we can see that even though the word immediately following the linking verb "become" is a an adjective ("astronomy"), it is not describing the subject of the sentence, it is describing the noun "major." Thus, it is not eligible to be the subject compliment. The next word to follow the linking verb, thus, is "major." Thus, this makes "major" the subject compliment.