选词填空 根据短文内容，从方框中选择恰当的单词完成句子并填写在答题卡对应的横线上。部分单词在填入前需进行词形转换,每个单词只能用一次,每空只能写一词。                                                                

      It is very    ____ to deal with the rubbish in cities. This is because rubbish not only pollutes the environment but also does harm to people's   ____ . We are trying to find some ways of dealing with the rubbish. First, the rubbish can be divided into different kinds. Newspaper and glass can be  ____ . Used tins can be made into beautiful handicrafts（手工艺品）. Polluted water is a big ____ . It must be dealt with properly before we let it flow into the river. Some harmful rubbish can be buried（埋）so that it will cause ____ pollution.

两个电阻R₁和R₂串联在电路中，R₁和R₂两端的电压之比2：3，若将它们并联在电路中，电阻R₁和R₂的功率之比为（　　）