①铜铝混合物 $\stackrel{足量盐酸}{\to }$ 充分反应测定生成气体的体积

②铜铝混合物 $\stackrel{足量氢氧化钠溶液}{\to }$ 充分反应测定剩余固体的质量

③铜铝混合物 $\stackrel{空气中加热}{\to }$ 充分反应测定所得固体的质量

④铁铝混合物 $\stackrel{足量盐酸}{\to }$ 充分反应测定生成气体的体积

以上方案可行的是（   ）

|-2|的值等于(  )

    In recent years advances in medical technology have made it possible for people to live longer than in the past. New medicines and machines are developing every day to extend life. However, some people, including some doctors, don't agree with these life extending measures, and they say that people should have the right(权利)t o die when they want, They say that the quality of life is as important as life itself, and that people should not be forced to go on living when conditions of life have become unbearable. They say that people should be allowed to die with dignity(尊严) and to decide when they want to die. Others don't agree and say that life under any conditions is better than death and that the duty of doctors is always to extend life as long as possible. And so the quarrel goes on and on without a definite(明确的) answer.