多数同学家里都有调光台灯、调速电风扇，过去是用变压器来实现上述调节的，缺点是成本高、体积大、效率低，且不能任意调节灯的亮度或风扇的转速．现在的调光台灯、调速电风扇是用可控硅电子元件来实现调节的，如图4所示为一个经过双向可控硅电子元件调节后加在电灯上的电压，即在正弦式电流的每一个周期中，前面的被截去，从而改变了电灯上的电压．那么现在电灯上的电压为      (　　)

下列命题中，假命题的个数有（   ）

1）无限小数是无理数；  （2）式子 $\sqrt{a}$ 是二次根式；

3）三点确定一条直线；  （4）多边形的边数越多，内角和越大．

某班利用节假日到江河中捡拾垃圾，这种做法（　　　）

①积极履行保护环境的义务　　　　

②有利于改善生态环境

③既是法定义务，又是道德义务　　

④是我国宪法和法律提倡的行为

选词填空

other, move, enough, find ,desert, make, use , another, friend , carry , trouble, friendly

You may think there is nothing but sand in the desert of the world, but it is not true. In the desert we can____ stones. We can see hills, too. There is a little rain in the ____  , but it is not____  for most plants.
　　The animals are ____ to the desert people in many ways. The desert people eat the meat and drink the milk of the animals. They use their skins to ____ shoes, water bags and even tents(帐篷). They use the camels(骆驼) for____  things.
The people of the desert have to keep ____  from places to place. They must always look for grass or desert plants for their animals. They usually live in the tents. When there is mo more food for their animals, they take down their tents, put them on the camels and move to ____ place. The desert people are very____ . No man in the desert would ever refuse to help the people in ____  and give them food and water

在平面直角坐标系中，点P（6，﹣5）在（　　）