完形填空     Do you drink bottle water? How long does it1you to drink a bottle of water? Maybe just five minutes. But the plastic (塑料的) bottle will stay in nature(大自然) for 500 years! Plastic does not disappear (消失) 2 It is a big3 for humans.     There are many plastic things in our lives. They are cheap, light and easy to make.     Every year, the world uses 500 billion plastic bags. Every minute, we buy 1 million plastic bottles. The plastic we throw4 in one year can circle (环绕) Earth5!     For plastic things, the trash can (垃圾桶) is not 6 place they go in their lives. Every minute, a full truck of plastic things7into the sea. They make the seawa ter 8.They are dangerous for sea animals, too, 9when they eat.     So, is there10 useful we can do to help? Here are some tips.(小提示) First, carry your own cup to school. Second, take cloth (布的) bags to shopping, and buy fewer new toys, or you can exchange toys with your friends. Yes, just these small things, then you can help make the world a better place.

他对我们很好, 但是他的妹妹却不是。

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如图所示，一束光在空气和玻璃两种介质的界面上同时发生反射和折射（图中入射光线、反射光线和折射光线的方向均未标出），其中折射光线（用字母表示）是____，反射角等于____度。

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往AgNO₃和Cu(NO₃)₂的混合溶液中加入一定量的铁粉，充分反应后过滤，向滤渣中加入稀盐酸有气泡产生，根据上述现象分析，下面结论错误的是（  ）

改革开放以来，中国政府执政兴国的第一要务是