Dictionaries say that “spring fever” is a lazy or restless feeling . People usually have the feeling on the first warm day of spring. Everyone has probably felt it at one time or another . people have talked about it for years.
   Recently, scientists have taken a good look at spring fever. What they found is quite surprising.
   In many places we live in , the winter months often seem dark and dreary. When spring comes late March , the world becomes colorful . The number of daylight hours grows with each passing day. According to many scientists, all the sunlight sets off chemicals in the brain (大脑). The chemicals make our feeling change and bring on spring fever.

化学“家庭小实验”是利用家庭日常生活用品进行化学学习和探究的活动，下列实验中用家庭日常生活用品能够进行的是（）
①检验纯碱中含有CO₃^2－
②除去热水瓶内壁上的水垢
③检验鸡蛋壳能溶于醋酸
④检验自来水中含有Cl^－