The correct answer is D because a function is a question that has exactly one answer.
If I pick a city, say NYC, and ask, “What are the professional sports teams in NYC?” there are more than one pro sports teams.
For this to be a function, there needs to be only one answer to the question.
Option A has only one answer to “How much electricity did this home use this month?”
Option B has only one answer to “What is ____ ranking right now?”
Option C is just weird, but the question of “How many hours are there in __ days?” has only one answer. (24 x the number of days)
Again, D has the possibility that a single city has more than one pro sports team.