某实验小组在探究“电流大小与哪些因素有关”的实验中：

    More than 6000 children were expelled（开除）from US schools last year for bringng guns and bombs to school，the US Department of Education said on May 8．
    The department gave a report on the expulsions（开除）as saying handguns accounted for 58 per cent of the 6093 expulsions in 1996—97，against 7 per cent for rifles or shotguns and 35 per cent for other types of firearms．
    “The report is a clear sign that our nation’s public schools are cracking down（严惩）”on students who bring guns to school，“Education Secretary Richard Riey said in a statement．“We need to be tough-minded（坚强的）about keeping guns out of our schools and do everything to keep our children safe．”
    In March 1997，an 11-year-old boy and a 13-year-old using hand-guns and rifles shot dead four children and a teacher at a school in Jonesboro，Arkansas．In October，two were killed and seven wounded in a shooting at a Mississippi school．Two months later，a 14-year-old boy killed three high school students and wounded five in Daducab，Kentucky．
    “Most of the expulsions，56 per cent，were from high schools，which have students from about age 13，34 per cent were from junior high schools and 9 per cent were from elementary schools．”The report said．

则W、X、Y、Z的金属活动性顺序为(   )

记某企业每天由空气污染造成的经济损失为S（单位：元），PM2.5指数为x．当x在区间0，100内时对企业没有造成经济损失；当x在区间（100，300内时对企业造成经济损失成直线模型（当PM2.5指数为150时造成的经济损失为500元，当PM2.5指数为200时，造成的经济损失为700元）；当PM2.5指数大于300时造成的经济损失为2000元．

附：

$K^2=\frac{n{\left(ad-bc\right)}^2}{\left(a+b\right)\left(c+d\right)\left(a+c\right)\left(b+d\right)}$ ，其中n=a+b+c+d．