________ is known to us all, our government has spared no efforts to control food prices.

A．What

B．Which

C．As

D．It

有下 * * 种物质：镁条、氧化钙、硝酸银。其中属于盐的是                      ，可用于制作节日焰火的是                   ，食品包装袋中可用作干燥剂的是                      。