Which describes how the underlined pronoun is used in the sentence? whom did you ask for directions? a. object of a preposition b. direct object c. subject d. predicate nominative

C subject thats the answer

 I think the answer is D: predicate nominative

A predicate noun is a word which renames the noun that has been mentioned in the sentence. In this case Franklin Roosevelt is the noun that has been renamed as "President", which makes it the answer to the question.
Another example in : My brother's favourite food is pizza.
The predicate nominative in the sentence is Pizza. because that is the word that is replacing the earlier mentioned noun, which was "food". 

It is the poet alfred, lord tennyson himself