Zhang Lin is a middle school student. He is a good boy. Uncle Wu lives next to him. Uncle Wu has no child and can't see anything. He works in the factory (工厂) near Zhang Lin's school. He goes to work at 7:30 in the morning and comes home at 4:30 in the afternoon. Zhang Lin walks to school at 8:00 in the morning and comes home at the same time as Uncle Wu in the afternoon. On weekdays Zhang Lin gets up early to take Uncle Wu to the factory. After school he takes him home. On Sundays Zhang Lin helps Uncle Wu clean the house and do some cooking. Uncle Wu thanks Zhang Lin very much. He says, “Zhang Lin is a good boy. He is like my son.”

读岩石圈物质循环示意图，图中数码表示变质作用的是（　　）

下图表示在18℃（a）和25℃（b）的池水中，水蚤的出生、死亡和种群大小的关系，图中的出生数和死亡数均为实际数量的两倍。下列有关水蚤种群数量变化的叙述正确的是