Write a multi-choice question for the following article, with the given choices and answer: Article: I made a promise to myself on the way down to the vacation beach cottage. For two weeks I would try to be a loving husband and father. Totally loving. No ifs, ands or buts. The idea had come to me as I listened to a talk on my car radio. The speaker was quoting a Biblical passage about husbands and their wives. Then he went on to say, "Love is an act of will. A person can choose to love." To myself, I had to admit that I had been a selfish husband. Well, for two weeks that would change. And it did. On arriving at the beach cottage, I kissed Evelyn meeting me at the door and said, "That new yellow sweater looks great on you." "Oh, Tom, you noticed", she said, surprised and pleased. Maybe a little puzzled. After the long drive, I wanted to sit and read. Evelyn suggested a walk on the beach. I started to refuse, but then I thought, "Evelyn's been alone here with the kids all week and now she wants to be alone with me." We walked on the beach while the children flew their kites. So it went. Two weeks of not calling the Wall Street firm where I am a director; a visit to the shell museum though I usually hate museums. Relaxed and happy, that's how the whole vacation passed. I made a new promise to keep on remembering to choose love. There was one thing that went wrong with my experiment, however. Evelyn and I still laugh about it today. On the last night at our cottage, preparing for bed, Evelyn stared at me with the saddest expression. "What's the matter?" I asked her. "Tom," she said in a voice filled with distress, "I don't?" "What do you mean?" "Well...that checkup I had several weeks ago...our doctor...did he tell you something about me? Tom, you've been so good to me...am I dying?" It took a moment for it all to be understood. Then I burst out laughing. "No, honey," I said, wrapping her in my arms. "You're not dying; I'm just starting to live." Options: A He praised her sweater, which puzzled her. B She insisted on visiting a museum, which he hated. C He knew something about her illness but didn't tell her. D He was so good to her that she thought she must be dying. Answer: D He was so good to her that she thought she must be dying. Question:
The author says, "There was one thing that went wrong with my experiment." What does "one thing" refer to?