为了探究某合金块浸没在水中所受浮力和它排开水的重力之间的关系，并借用水的密度ρ_水求出该合金块的密度ρ_x，某同学进行了如图甲、乙、丙、丁四次测量（弹簧测力计读数分别为F₁、F₂、F₃、F₄）．

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方程2x+a﹣4=0的解是x=﹣2，则a等于（   ）

    Hi, friends!My name is Jason．I am 11 years old and I live in Chicago in the USA．There are many holidays every year,and，my favorite one is Thanksgiving(感恩节)．It is a family holiday．

    Thanksgiving comes on the fourth Thursday of November every year．There is no school on Thanksgiving Day．That's great!My family gets together on Thanksgiving Day．My brother will drive home from New York．We always have a big dinner．My mom makes a lot of delicious food．My sister always helps her in the kitchen．We have roast turkey,sweet potatoes,pumpkinpie(烤火鸡，红薯，南瓜派)and so on．Turkey is a must in my family．Before dinner we give thanks to everything

wehave．

    I love this holiday very much．It teaches me to be thankful in life．My favorite thing about the holiday is being with my family and having a great time with them．That is a very important thing of the holiday．

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