Concrete nouns refer to those things or people that can be perceived by any one of our senses such as sight, taste, touch and smell. Abstract nouns denote an idea, a concept, a state of being and other such forms, which cannot be seen or experienced through any of our senses. Harishchandra is the name of a person, a body made of flesh and bone that can be seen and touched, hence it's a concrete noun. Truthfulness is the state of being truthful, hence it's an abstract noun. Option A has the correct forms of these nouns hence it's correct. Option B is incorrect because the former noun is not abstract, it's a person, not a concept or idea and the latter noun is not a physical body, it's a state of being. Similarly, option C is incorrect because Harishchandra is not an abstract noun, and option D is incorrect because truthfulness is not a concrete noun.