One fine afternoon, I was walking along Fifth Street when I remembered that it was necessary to buy a pair of socks. Why I wished to buy only one pair was unimportant. I turned into the first sock shop that caught my eye. A boy clerk, who could not have been more than seventeen years old came forward. “What can I do for you, sir?” he said. “I wish to buy a pair of socks.” I replied.

    His eyes shone. There was a note of excitement in his voice. “Did you know that you had come into the finest place in the world to buy socks?” I had no idea of that, as my entrance had been accidental. “Come with me,” said the boy, eagerly. I followed him to the back of the shop, and he began to pull down box after box from the shelves, showing their contents（内装物）for my choice.

    “Hold on, lad,” I said, “I am going to buy only one pair!” “I know that,” said he, “but I want you to see how beautiful these are. Aren't they wonderful!” There was on his face an expression of seriousness and pride and delight as if he were showing me the secrets of his religion（宗教信仰）. I became far more interested in him than in the socks. I looked at him in surprise. “My friend,” said I, “if you can keep this up, if this is not merely from having a new job, if you can keep up this high spirit and excitement day after day, in ten years you will own every sock in the United States.”

一个物体在水平面上以恒定的加速度运动，它的位移与时间的关系是x=24t－6t²，则它的初速度和加速度分别为（   ）

某学生做如下实验：第一步，在淀粉KI溶液中，滴入少量NaClO溶液，并加入少量稀硫酸，溶液立即变蓝；第二步，在上述蓝色溶液中，滴加足量的Na₂SO₃溶液，蓝色逐渐消失。下列叙述中对实验原理的解释和结论不正确的是（      ）