英语周报2020―2021八年级下册39期答案

A class pet is a wonderful addition to the class, which can develop children's responsibility, build a connectionand act as a motivator.(高分句型一)(要点1班级宠物的$k)But many factors need considering when choosing a class pet, including its size, cost, advantages and disadvantages(要点2选择班级宠物的要点) Birds and repiles are a poor choice because they are delicate andeasy to be harmed by children.(要点3不宜当选的宠物)A hardy fish can be an ideal class pet, for it,'s cheap, long-lived and easy to raise.(高分句型二)(要点4哈代鱼为个不错的选择)

7.C【解析】根据题干和线的信息可知,种群数量为S”型增长。在“S”型增长曲线中,K2之前种群增长速率随种群数量的增加而增大,K/2之后种群增长速率随种群数量的增加而减小;该种群曲线所示的任何时候都存在环境阻力;渔业捕捞后种群剩余量最好控制在K/2(种群增长速率最大),即S3点对应的种群数量;当种群数量为K/2时,种群增长速率最大,即S2点,此时(K值一种群数量)K值为0.50,并非最小值。故选C。

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