,

给出定义：若$m-\frac{1}{2}<x\le m+\frac{1}{2}$（其中m为整数），则m叫做离实数x最近的整数，记作{x}，即{x}=m在此基础上给出下列关于函数f（x）=|x﹣{x}|的四个命题：

①$f\left(-\frac{1}{2}\right)=\frac{1}{2}$；②f（3.4）=﹣0.4；

③$f\left(-\frac{1}{4}\right)=f\left(\frac{1}{4}\right)$；④y=f（x）的定义域为R，值域是$-\frac{1}{2},\frac{1}{2}$；

则其中真命题的序号是（　　）

2016年12月6日，我国首次发布《中国的中医药》白皮书。对于我国传统文化中的一个重要部分﹣中医药，我们的正确态度是（    ）

①继承优秀的传统的中医药事业       ②在实践中不断发展中医药事业

③中药有副作用，应该被放弃           ④全面继承中医药，拒绝引进西医

    It can be dangerous to travel by sea. Ships sometimes sink(下沉) far away from land. When this happens, the sailors(海员) have to get into small boats. If another ship does not come and help them and they do not have enough food or water, they will die.
    Most people believe we must not drink sea water. They believe that if we do, we shall be very ill because of all the salt in the water. A doctor called Alain Bombard did not believe this. He thought that people could stay alive by drinking sea water and eating small fish, animals and plants from the sea. On 19 October 1953, he set out in a small boat to cross the Atlantic Ocean(大西洋). He did not take any food or water with him.
    Every day Dr. Bombard drank just a little sea water. He also caught fish and they had water in them. He drank this water. He could not cook the fish, so he ate them as they were. He took small plants from the sea, which gave him more food.
Dr. Bombard became hot, tired and quite ill, but after 65days at sea he was still alive. He traveled 2,750 miles from one side of the Atlantic Ocean to the other, and on 24th,December 1953, he reached Barbados.
    He lost 20 kilos, but he showed that people could live on sea water, the animals and plants in the sea.