Answer and Explanation:
The appropriate relative clause to join the two sentences is "which belongs to my uncle."
So, the combined sentence would be: "This is the house which belongs to my uncle."
In this sentence, the relative pronoun "which" introduces the relative clause "which belongs to my uncle." The relative clause provides additional information about the house, specifying that it belongs to the speaker's uncle.
The use of the relative pronoun "which" helps connect the two ideas and provides clarity in describing the ownership of the house.