Here, we need to pay attention to certain details as in the case of reported and unreported speech and punctuation.
Option A -INCORRECT.
In this case, it would have been better if the author had made this option a ''reported'' speech on behalf of the professor. The punctuation sign just in front of ''professor'' is an unwanted one because it gave too much emphasis on the professor rather than the action that has been done. Also, the option here lacks any definition that could differentiate it from the original content.

Option B - INCORRECT.
It must be noted that from the option here, using the comma sign has largely given the needed description and broken the piece into understandable elements, such that the conjunction and at the end of the statement does not serve any other purpose or add any other information other than what's been said.

Option C - INCORRECT.
Here is a case of reported speech which saying is what the professor had said in class unfortunately, this option employed the use of unneeded punctuation as is the case with the comma sign applied after the student. It has broken the statement into other parts that's not needed.

Option D - CORRECT.
Here, the parts are well constructed. Being a Reported speech all the parts use conform i.e. in past tense. It gave the sentence a new dimension while retaining the original meaning.

Option E - INCORRECT.
Still the same shortcomings as noticeable in options A, B and C Above as Unnecessary punctuation. I t is thus evident that this option is also an INCORRECT one.