Here's why:
* Predicate Nominative: A predicate nominative is a noun or pronoun that renames the subject of the sentence. This sentence doesn't have a noun or pronoun that renames the subject.
* Predicate Adjective: A predicate adjective modifies the subject of the sentence and follows a linking verb. In this case, "beautiful" describes the subject "kimono." The implied linking verb is "is" (How beautiful *is* this kimono Keiko?)
Let me know if you'd like to try another example!