Respuesta :
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.