Given the task definition, example input & output, solve the new input case.
In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.
Example: Passage: Nearing London, Oliver encounters Jack Dawkins, a pickpocket more commonly known by the nickname the "Artful Dodger", and his sidekick, a boy of a humorous nature named Charley Bates, but Oliver's innocent and trusting nature fails to see any dishonesty in their actions. The Dodger provides Oliver with a free meal and tells him of a gentleman in London who will "give him lodgings for nothing, and never ask for change". Grateful for the unexpected assistance, Oliver follows the Dodger to the "old gentleman's" residence. In this way Oliver unwittingly falls in with an infamous Jewish criminal known as Fagin, the gentleman of whom the Artful Dodger spoke. Ensnared, Oliver lives with Fagin and his gang of juvenile pickpockets in their lair at Saffron Hill for some time, unaware of their criminal occupations. He believes they make wallets and handkerchiefs.
Output: Who believes Fagin's gang make wallets and handkerchiefs?.
This question is based on the following sentence in the passage "He believes they make wallets and handkerchiefs". It evaluates the understanding that the pronoun "he" refers to name "Oliver". You can ask questions like this one about most pronouns in a paragraph.

New input case for you: Passage: The United States has lost the war on drugs. Substance D, a powerful and dangerous drug that causes bizarre hallucinations, has swept the country. Approximately 20% of the total population is addicted. In response, the government has developed an invasive, high-tech surveillance system and a network of undercover officers and informants.
Bob Arctor is one of these undercover agents, assigned to immerse himself in the drug's underworld and infiltrate the supply chain. Sometime in the past, Arctor abandoned his wife and two children, leaving him alone in a now-rundown suburban house in Anaheim, California; the house has since been repopulated by Arctor's two drug-addicted, layabout housemates: Luckman and Barris. The three spend their days intoxicated and having long, paranoiac conversations. At the police station, Arctor maintains privacy by wearing a "scramble suit" that constantly changes every aspect of his appearance and he is known only by the code name "Fred." Arctor's senior officer, "Hank", and all other undercover officers, also wear scramble suits, protecting their identities even from each other.
Since going undercover, Arctor himself has become addicted to Substance D and has befriended the main woman he has been spying on: a cocaine addict and Substance D supplier named Donna. Arctor hopes to purchase large enough quantities of Substance D from Donna so that she is forced to introduce him to her own supplier, but he has also developed seemingly unrequited romantic feelings towards her.
Output:
What drug is Arctor's love interest hooked on?