Option D is the correct option. "Kind" is an Abstract noun. Abstract nouns are not capitalised. The name of the qualities of persons, animals, or things is known as an Abstract Noun. Noun is the name of a person, place, animal or thing. An Abstract noun denotes the name of ideas, feelings, quality or state rather than a concrete object. It names intangible items rather than tangible items. Examples of abstract nouns include kindness, strength, affection, hurt, anger, etc.