阅读下面文言文，完成后面小题。

蒲松龄著书（节选）

      蒲留仙先生《聊斋志异》，用笔精简，寓意蕴藉。相传先生居乡里，落拓^①无偶，性尤怪僻，为村中童子师，食贫自给，不求于人。作此书时，每临晨携一大磁罂^②，中贮苦茗，具淡巴菰^③一包，置行人大道旁，烟茗置身畔。见行道者过，必搜奇说异，随人所知；渴则饮以茗，或奉以烟，必令畅谈乃已。偶闻一事，归而粉饰之。如是二十余年，此书方告蒇^④。故笔法超绝。

      【注】①落拓：贫困失意，景况凄凉。②罂（yīng）：大腹小口的瓶或罐。③淡巴菰：烟草。④蒇（chǎn）：完成。

    I'm not much of a crier most of the time. But recently when I was reading a book on a plane, I started crying. Of course, it came as a big surprise when tears came up, no matter how hard I tried, I wasn't able to control myself.

    Oh no, not this now. I thought to myself. But even as the thought entered my brain. I felt the first hot drop of salty water coming down my face. I put my head down, hoping that I could go on reading.

    In fact, the harder I tried, the more tears pushed their way out of my eyes. You could guess how surprised the man next to me looked.

    I dropped my head in shame. He must think I was crazy. May be I could turn toward him, hold up the cover of the book and say in my crying voice. "I'm sorry, sir. It's just a really good book! "But I didn't say anything. Instead, I just put my head back against the seat and let the tears run. Do you know what decision I made while I was crying? My decision was that it was okay if he thought I was crazy. I'd rather be crazy than be the kind of person who wouldn't cry when the situation called for it, or who wouldn't let herself feel anything at all.

    I've been that girl who has spent so much time trying to make sure people didn't think I was crazy. But now I don't want to be that girl any more ---that bored and sad girl. I'd rather be this girl who is able to forgive(原谅), love and act, even if it means being disappointed or being hurt again and again.

美苏全面开展“冷战”的标志是什么？自从美国对苏联实行“冷战”政策以后，美苏之间出现了近半个世纪的“冷战”，没有发生“热点”。有人据此认为“冷战”是国际关系进步的一种表现。你同意这种看法吗？说说你的理由。

如图，等边△OAB的边OB在轴的负半轴上，双曲线$y=\frac{k}{x}$过OA的中点C，已知等边三角形的边长是4，则该双曲线的表达式为(    )