The best sentence that states a theme of "Rikki-Tikki-Tavi" is:
C. Too much pride can lead to conflict with others.
In "Rikki-Tikki-Tavi," the character Nag and his wife Nagaina demonstrate excessive pride, which ultimately leads to their downfall. Their prideful nature causes them to underestimate the abilities of Rikki-Tikki-Tavi, the mongoose, leading to a deadly conflict. The theme of pride leading to conflict is reinforced throughout the story, and the resolution demonstrates the consequences of such prideful behavior.
Therefore, the best sentence that states a theme of "Rikki-Tikki-Tavi" is: Too much pride can lead to conflict with others.