This isn’t supported, because we don’t have any evidence the critics think that mixing literary genres adds value to a narrative.

This isn’t supported, because we don’t have evidence the critics think Jacobs’ narrative compromised the goals of the domestic novel. They think it compromised the goals of a typical slave narrative, but they don’t necessarily think it compromised the goals of the domestic novel.

Not supported, because we don’t know that the critics think the reason Jacobs’ narrative allegedly favored the domestic novel has anything to do with the level of realism of a domestic novel.

Not supported, because we don’t know that the critics think the reason Jacobs’ narrative allegedly favored the domestic novel has anything to do with the level of sentimentality in a typical slave narrative.

This is the best answer. The critics think Jacobs’ narrative shortchanged the typical slave narrative because it conformed to the conventions of the domestic novel. This is evidence the critics believe mixing genres in one narrative might cause the goals of one of the genres (typical slave narrative) to be compromised. (”Compromise” in this context means impairing or hindering the achievement of something.)