Question

Which word in the sentence is a predicate nominative? Franklin D. Roosevelt was the only president of the United States to serve three terms.

president
three
terms
only

Could you explain why?

Answer 1

Nice.

Explanation:

Predicate nominative means subject and object refers same one.
Like It is I.

It and I are same that is is why grammar is it is I not me.
After auxiliary we need subject pronoun.

In our question Roosevelt and here president are the same parson who was elected three times for the president in the USA history.

president is a predicate nominative.
Another answer,

I am a teacher--here I and teacher refers same one.
Hope works