Is the underlined phrase an adjective phrase or an adverb phrase?

the true king of the beasts is the elephant.

a.
adverb phrase

b.
adjective phrase

According to the mla format, which best demonstrates the similarities and differences between the citations of a magazine and a book? both require the title and author, while magazines require the editor of the magazine. both require a date of publication, while magazines require the page number of the article. both require the format of the book, while books require the page number of the information. both require a location of publication, while books require the edition of the book if there is more than one.