20.(1)解:设点P(x0,y),由点P到F的距离比点P到x轴的距离大1,可得|PF|=地0+1,1分即y+=y+1,…2分所以p=2,即抛物线C的方程为x2=4y.…………………3分(2)证明:设A(n,y),B(x2,y2),直线AP的斜率为k心,直线BP的斜率为k,则A=2一(x≠x0),km=的一边(x2≠x0)…………………………………5分1-0x2-x0因为直线AP与直线BP的斜率互为相反数,所以kp=一kp,即二边=一边二6分2-x又点A(x,y),B(x2,y)均在抛物线上,可得,化简可得n+x2=-2xo,7分1=x02-0因为x=4,d=4m,所以一a=4y-y2),即二2=+2,…………8分故k9分因为=,所以y=x所以y=x………10分则k=x0.…11分故k+k=012分

读后续写Possible version lI stared at the paper and then looked around. I was cold. Although I could not see my sistersnor the new house, which was hidden from my sight by a grey wall, I got the feeling that I was notalone. Walking along the shore was a tall familiar figure who looked lost in his thoughts. I lookedgain at the paper in my hand, closed my eyes and wishedAs /opened my eyes, I found my father was standing right beside me. Happy birthday, sonhe said, patting my shoulder gently. I smiled up at him and took his hand. Looking back, life fromthat day on marked the start of a close bond and a strong friendship with my father. What was mybirthday surprise? Wishes do come truePossible version 2I stared at the paper and then looked around. On the backside, there was a map. I noticed thatit was clearly leading me in a direction, but who could have sent this? I stood there in silence andstudied it. I decided to follow the map and it led me down the beach until I reached a staircase. Iooked back and could no longer see my siblings. I continued to follow the point on the map, untilI unexpectedly lost my footing and fell zksq down the stepsAs I opened my eyes, I found my father was standing right beside me. Happy birthday, sonhe said, patting my shoulder gently. Then he asked how I had come upon this place? I explained tohim that I had found the bottle in the ocean and when I opened it had the words on it. Shocked bythe message, my father realized what I had found I threw this bottle into the ocean many years agowhen I was alone. he said. I used to come to this exact place to get away from everyone else. NowI get to share this experience with you. What a birthday surprise

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