中国的历史有多长,中国的茶就有多香.茶文化中有许多的物理知识,例如:
(1)绿茶看起来是绿的,是因为茶叶反射____ ;
(2)通过加热使新鲜茶叶中的水分快速____ ,这便是制茶业中的“杀青”;
(3)用沸水才能很快泡出茶香、茶色,这是因为温度越高,____ 越快.
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.
小勇继续调节滑动变阻器的过程中,小灯泡突然熄灭,电压表示数____(填“变大”、“变小”或“不变”),经检查发现灯丝烧断
12-7=____
22-7=____
42-7=____