题干

已知 {an} 是等比数列,且 an > 0 , a2a4+2a3a5+a4a6=25 ,那么 a3+a5= ____.
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5

同类题3

阅读选文,完成后面问题
蓓姬感到十分害怕,汤姆居然连往回走的路也找不着了。
“喂,汤姆,你怎么什么记号也没做!”
“蓓姬,我真笨!一个大笨蛋!我根本没想到还会顺原路返回!是的,我们现在迷路了。真是糟糕透顶。”
“汤姆,汤姆,我们迷了路!找不着路了!永远也走不出这个鬼地方了!真是的,我们当时干嘛不和别的伙伴一起走呢!”
说完,她一下子瘫在地上,大哭起来,这下子吓坏了汤姆,他以为她快要死了,要不然就是要发疯了。他坐在她旁边搂着她。她紧紧地挨着汤姆,脸贴在他怀里,一古脑地诉说她的恐惧,连后悔都来不及了,这声音传到远处变成了嘲笑,回荡在通道里。汤姆求她再打起精神来,可她说不能。于是汤姆开始了自责,骂自己不该把她弄到这种不幸的地步。这一骂倒有了好效果。她表示要努力抱定希望,只要汤姆不再说这种话,她愿意跟汤姆一起闯关,因为要说谁有错的话,她自己也不例外。
这样他俩又开始往前走,漫无目标地胡乱走——他们现在能做的就是往前走,不断地往前走。不久,希望又开始复苏——它没有什么理由,很简单,只是因为希望的源泉还没有因时间和失败而消失时,它自然而然地要复苏。
过了一会工夫,汤姆把蓓姬的蜡烛拿来吹灭,这种节约意味深长,言辞是多余的,不用多解释,蓓姬就明白了其中的含义,她的希望又破灭了。她知道汤姆口袋里还有一根整蜡烛和几个蜡烛头——但他必须节约着用。
又过了一会,疲乏开始袭上心头,可两个孩子尽力想置之不理,因为现在时间就是生命。他们连想坐下来休息一下都不敢想。只要往前走,往一个方向或者无论是往哪边走都算是前进,有可能会有结果;但千万不能坐下来,否则等于坐以待毙,好让死神降临得快些。
到后来,蓓姬柔弱的四肢再也支撑不住,她一步也走不动了。她坐在地上,汤姆也坐下来陪她休息。两人谈到家、那里的朋友、家里舒服的床铺,尤其是那灯光!蓓姬哭起来,汤姆想另换话题来安慰她,可是她已不止一次听到他这样鼓励,现在这些鼓励的话听起来倒像是在挖苦她。蓓姬实在疲乏极了,她昏昏欲睡,汤姆见此很高兴,他坐在那里盯着她看,只见她在甜蜜的睡梦中脸上的表情逐渐由绷紧状态变得舒展了,笑容也慢慢地露出来。那平静的脸庞给汤姆的心灵也带来了些慰藉。于是,他的心思转到了过去的时光和梦一般的回忆上去了,他陷入沉思时,蓓姬在一阵爽快的微笑中醒来,可是笑容突然中止,接着就是一阵呻吟声。
“唉,我怎么睡着了呢!要是一觉睡过去那该有多好啊!不!不!汤姆,我不是这么想的!不要这样看!我不说了。”
“蓓姬,你睡了一觉,这很好;你会觉得休息好了,我们会找到出去的路。”
“我们可以试试,汤姆。可我在梦中见到了一个美丽的国家,我想我们正是在去那儿的路上。”
“不一定,不一定。蓓姬,打起精神来!我们再去试它一试。”

同类题4

阅读理解

    It was a weeknight. We were a half dozen guys in our late teens, hanging around “the flat” — as usual. The flat was poorly furnished, which, after some time, grew tiresome. We wanted action.

    We got in a car, big enough for all of us to crowd into — and off we went, in search of adventure. We soon found ourselves at Blue Gum Corner, a place named after the huge old blue gum tree that stood by there, a well-known local landmark. It stands at a minor crossroad leading to our town. The trunk is tall and smooth with no handholds for climbing. About six metres from the ground the first branch sticks out over the road. We parked beneath the huge old tree and discussed what we might do. All of a sudden we hit upon an idea — a hanging! I was chosen as “hangee”.

    The plan was quite simple. As I stood upon the roof of the car, the rope (绳子) was threaded down my jacket through my collar and down one leg of my jeans. I put my foot through the loop at the bottom. There I hung, still. The boys rolled about laughing until, a car, I hear a car! Before they ran to hide in the nearby field, they gave me a good push so that “the body” would swing as the car drove by.

    To our disappointment, the car simply turned off for town without even slowing. The boys came out of their hiding places and we discussed the situation. Surely they had seen me, hadn't they? Then we heard another car. The act was repeated, but still without any obvious reaction. We played the game about five or six times, but as no one seemed to notice, we abandoned the trick.

    What we did not know was that every car that had passed had unquestionably seen “the body” and each one, too scared to stop, had driven directly to the local Police Station. Now at that time of the night, the local policeman was sound asleep in his bed, so the first person sent to the scene was the traffic officer that happened to be on duty that particular night. He had been informed that some person had been killed, by hanging, at Blue Gum Corner. When he arrived, the body was gone! And he was hearing “unnatural sounds” from the surrounding area. As far as he knew, some fierce animal was hiding in the field before him, possibly dragging a body behind him — and we thought we were scared!

    He went to his radio and made a call that really began to worry us. I lay so close that I could hear every word. He called for the “armed police” and a “dog team, better make it two” and he had a “serious situation” at Blue Gum Corner. Then the police officer arrived. After a briefing from the traffic officer he decided not to go into the field until armed police and dog teams arrived. Now two spotlights were on the field and none of us could move.

    As luck would have it, police cars cannot leave their spotlights on all night without charging their batteries. So, after a time, the two officers began lightening the field by turns, allowing us the opportunity to move on our fours for freedom. One by one, we all managed to steal away and make our way home. Behind us we left what must have looked like a small city of lights, police cars, roadblocks, barking dogs, armed officers and an old rope hanging from a tree.

    When I think back to that night, to that tree, to what the drivers of the cars think happened, to what police believe happened, and to what I know happened, I am reminded of a simple truth — our eyes see darkness and light, color and movement, our ears hear only vibrations (振动) in the air. It is how we explain these vivid pictures that shapes our “reality”.