Select the concrete noun(s) in the following sentence:
The child is the father of man.
A. child
B. father
C. man
D. all the above

Hint: A concrete noun is used to name the objects that are physically present and can be identified by any of our five sense organs.

Complete answer:
From the hint given to us, we know that a concrete noun is used to name the objects that are physically present and can be identified by any of our five sense organs. In the given sentence, we can identify child, father, and man as nouns respectively. All of them are the names that represent a stage of life, a relation, and species.
We already know that child is a noun. We can touch the child and see the child. Thus, we can identify its physical presence. Hence, option A is possibly the correct answer.
Father is the patriarch. We know that is a noun. We can touch the father and see the father. Thus, we can identify its physical presence. Hence, option B is possibly the correct answer.
Man is used to representing the human race. We can touch the man and see the man. Thus, we can identify its physical presence. Hence, option C is possibly the correct answer.
After having analyzed all three options, we observe that all three of them are correct.
 Hence, we can conclude that option D is the correct answer.
Note: Father also means male parent and man also means an adult male human being. However, in the given context of the sentence, that is, the sentence acts as a proverb, the other semantic meanings have been preferred.