下列除去杂质的方法正确的是（   ）

①除去乙烷中少量的乙烯：光照条件下通入Cl₂，气液分离

②除去乙酸乙酯中少量的乙酸：用饱和碳酸钠溶液洗涤，分液、蒸馏

③除去C₂H₆中少量的C₂H₄：气体通过盛有酸性高锰酸钾溶液的洗气瓶

④除去乙醇中少量的乙酸：加足量生石灰，蒸馏．

  已知图中的图形都是轴对称图形，总共有多少条对称轴？

 

为了发展生产力，我们必须坚持改革方向，用改革的办法解决发展中面临的深层次矛盾和问题。贯彻落实这一要求能使（  ）

①生产关系更加适应生产力的发展

②上层建筑适应经济基础的要求

③中国特色社会主义制度得到完善

④生产方式得到根本性的变革

下列式子：x²+2， $\frac{1}{a}$ +4， $\frac{3a{b}^2}{7}$ ， $\frac{ab}{c}$ ，﹣5x，0中，整式的个数是（   ）

   (One day Alice runs after a strange rabbit and comes into a deep hole. She becomes smaller when she wakes up the next day. She finds herself in a wonderland with many amazing things inside.)
   The Caterpillar(毛毛虫) and Alice looked at each other for some time in silence. At last the Caterpillar took the pipe out of its mouth, and said to her in a tired, sleepy voice.
   “Who are YOU?” said the Caterpillar.
   This opening for a talk couldn’t make Alice at ease. Alice replied, rather shyly, “I----I hardly know, sir, just at present ----at least I know who I was when I got up this morning, but I think I must have been changed several times since then.”
   “What do you mean by that?” said the Caterpillar, “Explain yourself!”
   “I can’t explain MYSELF. I’m afraid, sir.” said Alice, “because I’m not myself, you see.”
   “I don’t see.” said the Caterpillar.
   “I’m afraid I can’t put it more clearly.” Alice replied very politely, “for I can’t understand it myself. And being so many different sizes in a day is very puzzling.”
   “It isn’t.” said the Caterpillar.
   “Well, perhaps you haven’t found it so yet.” said Alice. “But when you have to turn into a chrysalis(蛹，茧)----you will some day, you know ----and then after that into a butterfly, I think you’ll feel it a little stranger, won’t you?”
   “Not a bit.” said the Caterpillar.
   “Well, perhaps your feelings may be different.” said Alice. “All I know is, it would make ME feel very strange.”
   “You!” said the Caterpillar scornfully. “Who are YOU?” The question brought them back again to the beginning of the talk. Alice felt a little angry because the Caterpillar was making such VERY short sentences. She drew herself up and said very seriously, “I think you ought to tell me who YOU are first.”
   “Why?” said the Caterpillar.
   Here was another puzzling question. As Alice could not think out any good reason, and as the Caterpillar seemed to be very unpleasant, she turned away.
   “Come back!” the Caterpillar called after her. “I’ve something important to tell you!”
   This certainly gave Alice some hope. Alice turned and came back again.