Which word in the sentence is a predicate nominative?

The busiest time of day has become the hour before bedtime.

a. bedtime

b. time

c. day

d. hour

A predicate nominative is a noun or a pronoun which follows the verb and describes the subject. In this case, the answer is D, "hour", because it immediately follows the verb, and as mentioned already, describes the subject, that is "the busiest time of day".