The correct answer is A. 1423.
The word “kindly” is an adverb that means “in a kind or generous way.” The word “book” is a noun that refers to a written or printed work consisting of pages bound together and having a cover. The word “return” is a verb that means to go or come back to a place or person. The word “the” is a definite article that is used to refer to a particular person, place, thing, or idea.
In the sentence “Kindly return the book,” the word “kindly” is used to emphasize the request that the book be returned. The word “book” refers to the specific book that is being requested to be returned. The word “return” refers to the action of giving back the book. The word “the” is used to refer to the specific book that is being requested to be returned.
The other options are incorrect because they do not make sense in the context of the sentence. Option B, 1342, is incorrect because the word “book” comes before the word “return.” Option C, 1243, is incorrect because the word “return” comes before the word “the.” Option D, 4123, is incorrect because the word “the” comes before the word “book.”