题目

Women who own cats are more likely to have mental health problems and kill themselves because they can be infected by a common parasite(寄生虫) that can be caught from cat litter(猫砂), a study has found.Researchers found women infected with the Toxoplasma gondii (T. gondii) parasite(刚地弓形虫), which is spread through contact with cat waste or eating undercooked meat or unwashed vegetables, are at increased risk of attempting suicide.The study involved more than 45,000 women in Denmark. About a third of the world's population is infected with the parasite, which hides in cells in t在科学研究中，往往要把一个较大的课题分解成若干个小的子课题来分别进行研究。在“观察生长素对植物生长发育的影响”这一研究性学习课题中，某小组同学选用生长素类似物吲哚丁酸（IBA）进行如下实验：①取生理状况相同的相同植物的三组带芽的枝条甲、乙、丙，每组10支；②将甲、乙、丙组枝条的下端分别浸泡在下表所示的溶液中，相同时间后，扦插在潮湿的沙土中，在适宜的环境中培养。枝条甲组乙组丙组溶液5×10-5g/mL的IBA溶液5×10-1g/mL的IBA溶液清水③一段时间后，观察甲、乙、丙组枝条的生根情况，统计每组枝条的平均生根数量，绘制得坐标如下。据图回答：他们的子课题名称是不同浓度吲哚丁酸对扦插枝条生根的数影响。（1）设置清水组的目的是______________________。（2）本实验中的自变量是______________________。（3）实验结果是___________组枝条生根最多，___________组枝条生根最少。（4）实验说明生长素类似物的作用特点表现为___________。