Choose the correct meaning of the underlined idiom in the given sentence.

Blue blood is not necessarily a guarantee of one’s public decorum.

A person belonging to a high family

The correct meaning of the underlined idiom in the given sentence is (4) A person belonging to a high family.

The idiom "blue blood" refers to people of noble or aristocratic birth. It is often used to describe someone who is from a wealthy and privileged background.

In the given sentence, the speaker is saying that even people from high families can behave badly in public. This is because blue blood does not necessarily guarantee good manners or good behavior.

The other options do not fit the meaning of the idiom.

• A person belonging to a middle-class family is not considered to be blue blood.
• A person belonging to an honest family is not necessarily from a high family.
• A person belonging to a poor family is not considered to be blue blood.