题目

The United States is already one year into a depression That was the news this week from the Na-tional Bureau of Economic Research. The downturn is the longest since a depression that began in 1981and lasted sixteen months. Economists generally wait for production to shrink for six months in a row before they declare a re-cession. But the bureau, a private group, uses a wider set of information to measure the economy. Thenews only confirmed what many people already knew: that the world's largest economy is weak and maynot recover soon. Worsening conclitions have led to a big drop in sp关于氧气，根据信息写出对应反应的文字表达式（要求所选反应不能重复）．实验室用氯酸钾和二氧化锰制取氧气；铁在氧气中燃烧的反应；硫在氧气中燃烧的反应；红磷在空气中燃烧的反应 ．