Mrs. Higgins is a humble lady.

The correct answer is D. unassuming.

An unassuming person is modest and not proud. They do not seek attention or praise, and they are content with what they have. Mrs. Higgins is described as being humble, which means that she is modest and not proud. She is not interested in showing off or being in the spotlight. She is content with her life and does not need to prove anything to anyone.

The other options are incorrect because they do not describe Mrs. Higgins’s personality.

• Whimsical means to be fanciful or imaginative. Mrs. Higgins is not described as being fanciful or imaginative.
• Youthful means to be young or to have the characteristics of youth. Mrs. Higgins is not described as being young.
• Vain means to be excessively proud of oneself. Mrs. Higgins is not described as being proud.