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: Simon is a decent fellow, married to a lovely woman Pam, living comfortably with two children. He has grown tired of the lack of sex and is attracted to a cellist friend of his wife, Katrien. 
Katrien travels to New Zealand to follow her husband Klaus in an attempt to rekindle their marriage. However, she catches him in bed with a young arts student and so their marriage collapses. Katrien, now available and lonely from the breakdown of her marriage, is susceptible to Simon's attraction.The two become fascinated with each other, but don't immediately start an affair. She doesn't want to destroy his greatest appeal, which is that he is upright and reliable. They eventually attempt some meetings, but something always goes wrong. Either he arrives late and the children are coming, or he ejaculates prematurely. 
Opportunity comes when they discover that they are both going to be in Germany the same week. Simon books a hotel room in Berlin, where he and his boss are attending a convention. Katrien comes to his room, but before they manage to have sex, his wife surprises him by showing up. Katrien escapes to an adjacent room through an interconnecting door and Simon and his wife make violent love, which Katrien hears through the wall. She gets upset because they were just about to have sex and he is having sex with his wife. 
Pam sees Simon sneak into the hallway during a speech and hears Katrien's voice on the other end of his phone, figures out what they are doing, and flies back to Wellington angry. She soon asks for a separation.
Output:
What is the name of the person Katrien is friends with?