如图所示，电源电压U＝6V且保持不变，R₁＝10Ω，R₂是最大阻值为60Ω的滑动变阻器，L是标有“6V  0.72W"字样的灯泡，灯泡灯丝电阻不变．

（1）当R₂的滑片P到最左端时，要使灯泡L正常发光，S₁、S₂各应处于什么状态?
（2）当S₁、S₂都断开，5分钟内灯泡L消耗的电能是多少?
（3）调节滑动变阻器滑片，闭合S₁、S₂，当电流表示数最小时，整个电路消耗的电功率是多少?

     Tony Wheeler was born to travel. His father worked for an airline. For the first 16 years of his life，Wheeler and his family lived in many different countries.
     In the early 1970s，Wheeler met a young woman named Maureen. They soon married. Before getting jobs， Tony and Maureen wanted to travel. They took a year-long trip from London，through Asia，to Australia. On the trip，they visited places like India， Iran， and Afghanistan.
     When Tony and Maureen arrived in Australia，people asked many questions about their trip. To answer these questions，Wheeler wrote a guidebook called Across Asia on the Cheap . The book told people about different countries' weather，customs(风俗），and places to see. But unlike travel guides in the 1970s，Wheeler’s book also talked about places most tourists did not go. He also wrote about unusual things to see and do. The book was very popular．
     Wheeler and Maureen started a company called Lonely Planet. They continued travelling. They wrote guidebooks for each place they visited. Today，400 people work for Lonely Planet. The company has over 650 guidebooks. Wheeler still writes about travel “hot spots” (for example，Cambodia in Asia and Croatia in Europe). For more information，read the books!

如图所示是一种水位自动报警器的原理图，水位到达A时该报警器自动报警，此时

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①有利于我国商品出口和引进外资        
②有利于我国商品进口和对外投资

③说明经济全球化使世界经济发展不平衡  
④说明经济全球化使各国经济联系在一起

设向量$\overrightarrow{a}$，$\overrightarrow{b}$满足|$\overrightarrow{a}$+$\overrightarrow{b}$|=$\sqrt{10}$，|$\overrightarrow{a}$﹣$\overrightarrow{b}$|=$\sqrt{6}$，则$\overrightarrow{a}$•$\overrightarrow{b}$=____