函数$f\left(x\right)=\sqrt{3}\tan (\frac{x}{2}-\frac{\mathrm{\pi }}{4})$,$x\in R$的最小正周期为（   ）

读某地区人口出生率、死亡率变化图和人口年龄结构变化图，完成问题．
 
按联合国标准，如果一个地区＞65岁的人口达到7%，则可视为进入老龄化社会．该地区开始进入老龄化社会的时间是（ ）

①生命的接续，使得每个人的生命不仅仅是“我”的生命，还是“我们”的生命     ②在生命的传承关系中，我们能更好地认识和面对自己的生命

③在生命的传承关系中，我们只是延续了血脉的发展                                          ④在生命的传承关系中，美玲只是两个民族的发展果实

阅读理解

A

　　 Dolphins (海豚) are not fish but mammals (哺乳动物)．They live in groups, and speak to each other in their own language. In this way they are like many other animals, like bees. But dolphins are very different from almost all land animals. Their brain (脑) is nearly the same size as humans', so they are the cleverest animals. And they live for 20 to 30 years.

        But what does the dolphin look like？The dolphin has teeth, and eats fish. It can grow up to three and a half metres long. Its nose is very long. Like some other animals, the dolphin uses sound to find its way. They make sound to talk to each other and to help find food. We now know they don't use their ears to listen to the sound, but the jaws (颚)．

　　　Dolphins are friendly to people. They often save people in the sea. So many people like them.