In Chapter-9, Dr. Lanyon expresses how horrified he is with the news of transformation. He strictly refuses to witness it because he does not want to bend his scientific values and beliefs. We can say that the transformation of Dr. Jekyll was horrific for Lanyon to face and one can easily snap an idea of, why he died at the end of the plot. Therefore, the appropriate choice is "option-b", Jekyll changing to Hyde, which badly disturbs Dr. Lanyon.