Final answer:
Emphasizing the word 'house' in the given sentence likely serves to create a contrast between the divided physical structure and the unity of a family, making 'contrast' the correct answer.
Step-by-step explanation:
The bolded word "house" in the statement "A house divided against itself cannot stand, but a family will preserve," when emphasized in speaking, can change the meaning conveyed by the speaker. The emphasis on the word "house" could signal a contrasting relationship between a physically divided structure and the unity of a family. Therefore, the vocal emphasis on "house" is most likely to illustrate the contrast.