关于某无色透明溶液中所含离子的鉴别，下列叙述正确的是（ ）
A：加入Ba(NO3)2溶液，生成白色沉淀，加稀盐酸沉淀不消失，则原溶液中一定有SO42–
B：通入Cl2后，溶液变为黄色，加入淀粉液后溶液变蓝，则原溶液中一定有I–
C：加入盐酸，生成的气体能使饱和的澄清石灰水变浑浊，则原溶液中一定有CO32–
D：加入NaOH溶液并加热，产生使湿润的蓝色石蕊试纸变红的气体，则原溶液中一定有NH4+
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．
能在纸张、布匹上留下 “油斑”的物质是 （ ）。
下列事件发生的先后顺序排列正确的是( )
①西安事变 ②红军长征 ③九一八事变 ④日军占领东三省
俗话说“食不言，寝不语”，其实吃饭时不能大声谈笑是有科学道理的，原因是（ ）
