了解安全知识，可以更好地保护人身和财产安全．下列做法正确的是（　　）

A．发现天然气泄漏应立即开窗通风，并关闭阀门

B．用防腐剂亚硝酸钠腌渍鱼肉和蔬菜

C．用过量的添加剂增白面粉

D．用甲醛浸泡海产品保鲜

He asked ___   for the overcoat.  [      ]

A. how much has my sister paid    

B. how much my sister has paid    

C. how much did my sister pay    

D. how much my sister paid