一般家庭是利用冰箱来保鲜水果、蔬菜．利用你学过的生物知识，试着分析冰箱能延长果蔬储存时间的主要原因是（　　）

Every year people celebrate the Spring Festival in China．Usually it is in January or February．It's the most important(重要的)festival in China．So before it comes，everyone buys many things，and they often make a special kind of food called dumplings-It means"come together"．Parents always buy new clothes for their children and children also buy presents for their parents．On the Spring Festival eve(除夕)，all the family members come back home. They sing, dance and play cards．When they enjoy the meal，they give each other the best wishes for the coming year．They all have a good time。

正常情况下，人类女性卵细胞中常染色体的数目和性染色体为

如图所示，甲、乙两图的读数依次是____ ℃，　____ s．