In the sentence, "The dog ran into a store that had its door open." What is the relative pronoun?

A. Dog
B. Ran
C. Into
D. That

D. That

D. That

The relative pronoun in the given sentence is "that."

To identify the relative pronoun, you need to look for a word that connects a dependent clause to its antecedent (the word that the dependent clause is referring to). In this sentence, the dependent clause is "that had its door open," and it is connecting to the noun "store." The word "that" introduces the dependent clause and acts as the relative pronoun.

So the correct answer is D. That.