为节约用水，小华为农场的储水箱设计了一个自动抽水控制装置。如图，水箱高为1m，容积为0.8m3 。在空水箱底部竖直放置一重 5N 的长方体， 长方体高为 1m、 底面积为 0.02m2 ，上端通过绝缘轻杆与路的压敏电阻 R 接触， 此时压敏电阻受到的压力为零。 压敏电阻 R 的阻值随压力 F的增大而减小， 部分数据如下表。 控制电路电源电压 U=12V， 定值电阻 R 0 为保护电阻。 当控制电路的电流 I≥0.5A 时， 电磁铁将衔铁吸合， 工作电路断开， 水泵停止给储水箱抽水控制电
（1）2A；（2）10Ω；（3）3900J
Dogs are the best pets of humans. They come in all sizes. Some dogs are as small as a football, and others are as tall as a desk. Dogs’ fur (毛) is different, too. It can be long and soft, or smooth and hard. People don’t mind the kind of fur, because all dogs are good to hug.
请在字典中查一下这个词。
我喜欢甜食， 你知道的。
去年， 彼得在旅途中和许多人交了朋友。
我叫托尼· 史密斯， 史密斯是我的姓。
我们在课上回答问题时应该起立
Tea and coffee are two of the most popular drinks in the world. However, people usually like one more than the other. These drinks also have very different uses.
People in the office usually sit for most of the day when they work. But this is bad for a person’s health. When people sit for too long every day, they don’t move very much. So it is easy to start getting fat. Sitting too long is also bad for their work because it makes them want to sleep. When this happens, people may make more mistakes in their work or spend more time finishing their work. Companies need workers to be healthy, so how do they fix the problem?
