①要坚持矛盾普遍性与特殊性的辩证统一

②矛盾双方既对立又统一推动事物的发展

③矛盾同一性是推动事物发展的根本动力

④矛盾主要方面和次要方面是相互依存的

F₁,F₂ 是椭圆$\frac{x^2}{9}+\frac{y^2}{7}=1$的两个焦点，A为椭圆上一点，且$\angle A{F}_1{F}_2={45}^{°}$，则$△A{F}_1{F}_2$的面积为(      )

    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．