It has been proved _________eating vegetables in childhood helps to protect you against serious illnesses in later life.    [ ]

A. if          

B. because      

C. when    

D. that

为适应火车提速，沪宁线上原有的短轨已全部连接为超长轨．工程技术人员先点燃镁条，镁条燃烧产生大量的热使铝热剂（铝粉和氧化铁粉末的混合物）在高温下发生反应，生成熔融状态的铁，从而焊接钢轨间的缝隙．写出生成熔融状态铁的化学方程式______，其中还原剂是______，其基本反应类型是______．