Concept:A well-defined set has a clear, common property that allows us to decide whether an object belongs to it.
Explanation:Option A contains unrelated items: a person, a person, a colour, and a number.
Option B also mixes different categories: ink, fruit, colour, and an object.
Option C mixes a vehicle, a road, glass, and a book, which are not similar.
Option D contains only names of people: Seth, Mary, Jacob, and Evelyn.
So only Option D has a single clear category of elements.
Hence, it is the well-defined set.
Answer:D. {Seth, Mary, Jacob, Evelyn}