You are given a sentence and a question. You're expected to write the correct answer based on the sentence.

Sentence: Tim has to push an ice sculpture across the ballroom in order to get his restaurant ready for a wedding. He notices that it is easier to push the sculpture when he moves it across the polished ballroom floor than when he moves it across the rough cobblestone floor. Question: If Tim is trying to keep the ice sculpture from melting, which surface should he push it across in order to produce less heat?
ballroom floor