题目

某种群死亡率如图中Ⅱ曲线，出生率如图中Ⅰ曲线，则在哪一时期此种群的个体总数达到其生活环境负荷量的顶点       ( ) A．a B．b C．c  D．d   答案：C题图中曲线Ⅰ、Ⅱ分别代表出生率、死亡率，当种群数量达到最大值时，出生率等于死亡率，此时种群增长率为0。  任务型阅读。阅读下文并回答问题。The students were having their chemistry class. Miss Li was telling the children what water was like. After that, she asked her students,“What's water?”No one spoke for a few minutes. Miss Li asked again, "Why don't you answer my question? Didn’t I tell you what water is like?”Just then a boy put up his hand and said, “Miss Li, you told us that water has no color and no smell. But where to find such kind of water? The water in the river behind my house is always black and it has bad smell.”Most of the children agreed with him.“I'm sorry, children.”said the teacher,“Our water is getting dirtier and dirtier. That’s a serious problem.”根据短文内容，回答问题。1.Did the teacher tell the students what water is like?2.What did the teacher tell the students water is like in chemistry class?3.Why does the water in the river have color and smell?