题目

A small piece of fish each day may keep the heart doctor away. That’s the finding of a study of Dutch men in which deaths from heart disease were more than 50 percent lower among those who consumed at least an ounce of salt-water fish per day compared to those who never ate fish. The Dutch research is one of three human studies that give strong scientific support to the long held belief that eating fish can provide health benefits, particularly to the heart.  Heart disease is the number-one killer in the United States, with more than 550,000 deaths occurring from heart attacks each y将铁粉加到一定量AgNO3、Cu(NO3)2的混合溶液中，充分反应后过滤，向滤渣中加入稀盐酸发现有气体逸出，则滤渣的组成成分是（    ）A．铁        B．铁和铜         C．铁、铜、银         D．铁和银