以下化学药品保存或实验操作正确的是（ ）

A．保存浓盐酸

B．保存固体氢氧化钠

C．稀释浓硫酸

D．点燃酒精灯

Evdence has been found through years of study         children’s early sleeping problem are likely to continue when they grow up.

A．why

B．how

C．whether

D．that