为了监督司机是否遵守限速规定，交管部门在公路上安装了固定测速仪．如图所示，汽车向放置在道路中间的测速仪匀速驶来，测速仪向汽车发出两次短促的超声波信号．第一次发出信号到测速仪接收到经汽车反射回来的信号用时0.5s，第二次发出信号到测速仪接收到经汽车反射回来的信号用时0.3s，若发出两次信号的时间间隔是1.1s，超声波的速度是340m/s．则（      ）

如图所示的电路，R₁=30Ω，R₂=10Ω，开关S闭合后，电流表A的示数为0.4A，求：

（1）电源电压．

（2）通过R₂的电流．

（3）干路中的电流．

    The film is very exciting and dramatic(戏剧性的), but it is also romantic(浪漫的) and very sad. It is about the ship, the Titanic, which sank in the Atlantic in 1912. It is a love story. The two famous stars are Leonardo Di Caprio and Kate Winslett. They fall in love on the ship, but are not allowed to be together as she is rich and he is poor. Leonardo is excellent as poor, handsome Jack and Kate Winslett is perfect as rich and beautiful Rose. The best thing about the film is the part where the ship is sinking. This love story doesn't have a happy ending.

    Flubber is a comedy. Starring(主演) Robin Williams is a forgetful scientist. He is very forgetful and he even forgets his own wedding(婚礼)! Flubber is the name of the amazing(令人惊奇的) green stuff(物品) that he invents. The plot(情节) is about two bad men who try to steal both Flubber and the scientist's girlfriend. The scientist has lots of silly adventures(历险) with Flubber, and he is really funny as the mad scientist. The best thing about the film is the special effects as Flubber changes into all different shapes and sizes and even does a dance routine(舞蹈动作). It's really an enjoyable film.

根据短文内容，完成表格。