Select the most appropriate meaning of the underlined idiom in the given sentence.
Only those having blue blood can dethrone the evil autocrat and restore equilibrium.

The correct answer is Aristocratic lineage.

Explanation:
The idiom blue blood refers to noble, royal, or aristocratic ancestry or lineage. Historically, the phrase originates from the Spanish expression sangre azul, which was used by aristocratic families who claimed nobility based on having pale skin, through which their veins appeared blue compared to the working class who worked outdoors in the sun.

In the given sentence, "Only those having blue blood can dethrone the evil autocrat and restore equilibrium," the idiom describes individuals belonging to a high social class or noble birth line.

Breakdown of Options:
• Political ideology: Refers to a set of ethical ideals, principles, or doctrines, which does not match the idiom's meaning.
• Vigilant nature: Refers to being watchful, cautious, or alert, which is unrelated.
• Aristocratic lineage: Refers to noble birth or royal descent, which is the exact and correct meaning of blue blood.
• Bitter relations: Refers to animosity or hostility, which is incorrect.