题干

图示为理解某些生物学问题所建立的一个数学模型(此图仅表示一定条件下的变化趋势).下列不能用此数学模型表示的为(   )

A:若x表示外界O2浓度,y表示CO2释放量,则a为有氧呼吸强度,b为无氧呼吸强度

B:若x表示进食后一段时间血糖浓度,y表示激素含量,则a为胰岛素,b为胰高血糖素

C:若x表示生长素浓度,y表示生理作用,则a为对根的促进作用,b为对茎的促进作用

D:若x表示时间,y表示种群数量,则a可表示竞争中的优势种群,b可表示劣势种群

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C

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    Jia Zuosheng, 27, used to work as a security guard (保安) at the library of Tsinghua University. But a few months ago, he became a college student in Lishan College in Shandong and he studies math there now. When hearing this news, many people were surprised. On school opening day, many reporters waited outside the school gate to interview him.

    “I was born in a poor village in Shandong Province," said Jia. "Our village has never had a college student. Most boys work in town after growing up. I failed the National College Entrance Exam(高考)twice. Then I went to Beijing to find jobs. In the following years, I went on studying by myself while working.”

    At the end of 2009, Jia found a job as a security guard at the library of Tsinghua University.“I cherished (珍惜) the job very much because it gave me a good chance to read books," Jia said.“I usually worked at night so I had plenty of time to study in the daytime.” When he had problems that he couldn't work out, Jia asked the students at Tsinghua for help. "My dream is to be a college teacher. So I need further education. That's the reason why I took the National College Entrance Exam again," Jia said. “I wish to educate students with my knowledge and love and help them enjoy true, kind and beautiful things.”

    Jia's mother said Jia has always been independent(独立的)and knows what he wants. But she has other worries. "It's difficult to find such a good job at present as a library guard in Tsinghua University. I'm not sure if this is a right decision.” “I will never regret(后悔),”said Jia. "Everyone will have a new start. It's the end, and the beginning.”