如图中属于变压器的是（   ）

DNA分子的双螺旋结构中遵循碱基互补配对原则的是（　　）

造成黄土高原水土流失严重的人为因素主要是（　　）

    In our city there are more and more cars and buses on the roads. Many people drive to work .First, it's good to have a car. You needn't to wait for the bus. You can go to work on time. Then ,there are many busy roads in the city . Can you drive safely? Traffic lights are very important. You must look at the traffic lights and wait for the green man. If someone is crossing the road, you must stop your car and look carefully. We must follow the rules and stay safe on the road.