已知一元二次方程x2-2x-1=0的两个根是x1、x2，则x1+x2=_____

具有缓冲血压波动功能的血管是

A．主动脉
B．微动脉
C．毛细血管
D．静脉

A good memory is a great help in learning a language. Everybody learns his mother language when he is a small child. 1)He hears the sounds,① ______them and then he learns to_____. Some children are living with their parents in foreign countries. ②They can learn two languages as easily as one because they hear, remember and speak two languages every day. In school it is not so easy to learn a foreign language because the pupils have so little time for it, and they are busy with other subjects, too. But your memory will become better and better when you do more and more exercises..

小题1:在①处填入适当的词 ____________  _____________

小题2:将②句划线部分译成中文.

___________________________________________________

小题3:回答问题：How do you improve your memory?

___________________________________________________

小题4:在文中找出同意句：

A foreign language is hard for the pupils to learn because they almost have no time at school.

____________________________________________________

小题5:找出或写出本文的中心句.

________________________________________

下列各组地形区，全部位于我国北方地区的是  （   ）

A．云贵高原、黄土高原

B．东北平原、华北平原

C．云贵高原、东北平原

D．四川盆地、华北平原

空气吹出法工艺，是目前“海水提溴”的最主要方法之一。其工艺流程如下：

（1）溴在周期表中位于________周期__________族。

（2）步骤①中用硫酸酸化可提高Cl₂的利用率，理由是___________________________。

（3）步骤④利用了SO₂的还原性，反应的离子方程式为__________________________。

（4）步骤⑥的蒸馏过程中,温度应控制在80～90℃温度过高或过低都不利于生产，请解释原因____________________________________________________。

（5）步骤⑧中溴蒸气冷凝后得到液溴与溴水的混合物，可利用它们的相对密度相差很大的特点进行分离。分离仪器的名称是______________________________________。

（6）步骤①、②之后并未直接用“含Br₂的海水”进行蒸馏得到液溴，而是经过“空气吹出”、“SO₂吸收”、“氧化”后再蒸馏，这样操作的意义是_______________________。

混合料预热的方法有哪些？