完形填空

    Bike-sharing is a new choice for short journeys in cities．It is good to the1development of the big cities．

    A2by a company found that shared bikes started the nation's3for bikes again．Now more and more Chinese people are4bikes instead of cars to make short journeys in cities．

    An engineer of that company says that since the5of shared bikes，people have made fewer trips by car．The love for shared bikes is not only among 6people，who were born in the 1980s and 1990s，but also among people over sixty．

    At weekends，the number of the riders in Shenzhen reaches the7of all cities．On weekdays，the number of people who use shared bikes to travel to word is8in Shanghai．

    It is said that bike﹣sharing will help9the cities'environment．It not only helps solve the traffic problems，but also will help to make more use of10in cities．Take Beijing as an example if more people choose shared bikes，an area of five Bird's Nest stadiums （体育场）will be saved．

表是生物学工作者收集到的某湖区几种生物的食物网关系（“√“表示存在食物关系）．请据表和图回答问题：

（1）该生态系统的结构包括____ ．此生态系统中共有____ 条食物链，在该食物网中鲫鱼占有____ 个营养级．

（2）若由于某种原因螺蛳全部死亡，该湖泊生态系统的抵抗力稳定性将____ 

（3）假如鲫鱼的食物有$\frac{1}{5}$来自轮虫，$\frac{1}{5}$来自螺蛳，$\frac{1}{5}$来自水草，$\frac{2}{5}$来自绿藻，能量流动效率按10%计算，该鲫鱼增重2kg需消耗绿色植物____ kg．

（4）如图是对某地引进经济鱼进行种群密度调查后绘出的种群增长速率曲线．调查该经济鱼种群密度常用的方法是____ ，在t₂时期该鱼的种群数量是该河流对该鱼的____ 

（5）鸡粪是优良的鱼类饲料，适量的投入可以给鱼提供食物，从而提高鱼的产量．鸡粪中的碳元素只能以____ 形式流向鱼．向河流中少量投入鸡粪对生态系统不产生明显的影响，这是因为该生态系统具有____ 

（6）据研究表明绿藻含有人体所需的几乎全部的营养成分，还可以提高人体的免疫力和抵抗力，则说明生物多样性具有____ 价值．

已知$a\in R$,则“$a<2$”是“$a\left|a\right|<1$”成立的(     )