Answer:
c. Being among the trio who witness the transformation of Mr. Hyde into Dr. Jekyll
Step-by-step explanation:
Dr Lanyon was taken into confidence by Dr. Jekyll for his transformation as he himself is also a doctor who can procure the ingredients for Jekyll's potion to transform into Hyde. But when he saw the true nature of the transformation, he became mortally ill. It was too much for him. Lanyon embodies the rational and skeptic nature of what the world should be against the metaphysical nature of what Jekyll is trying to achieve and had done so. His death can be said to be due to the witnessing of Jekyll's transformation into the monstrous Mr. Hyde.