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    Welcome to Class 4, Grade 7. This is our classroom. There are twenty boys and twenty -four girls in the classroom. The teacher's desk is in the front of the classroom. There is a big blackboard on the front wall and a small blackboard on the back wall. There are two maps on the wall. One is a map of China and the other is a map of the world．There are some photos on the wall. There are some flowers by the windows. Our classroom is very beautiful.

在“测量小灯泡的电功率”实验中，小灯泡额定电压为2.5V（电阻值约为5Ω）。