The correct option is D C
Let’s examine the sentence: “I do not know what have you done with your pen.” The sentence is in a form of statement and not a question. Hence, the helping verb, “have,” would not come after “what,” as this is required in the structure of a question. Since, the given sentence is a statement, the helping verb “have” would come after the pronoun, “you.” So, the correct sentence would be, “I do not know what you have done with your pen.” So, the error is in Part C of the sentence. Hence, Option C is the correct answer.