Answer:
a. A potion, concocted by Jekyll.
Step-by-step explanation:
Robert Louis Stevenson story of "The Strange Case of Dr. Jekyll and Mr. Hyde" is a fictional narration of a doctor with an alter ego. This another person is a monster kills people while the real initial person is a caring doctor.
In this Scottish Gothic novel, the character of Dr. Jekyll had concocted a potion that enables him to transform into another person, but a monstrous Mr. Hyde. They are opposites in their characters. While the first is a doctor, well liked and respected by everyone while the other is a monster who kills people. In the end, Dr. Jekyll killed himself with poison, thus removing the murderous Mr. Hyde along.