一些故事影片中常有这样的镜头：高墙倒塌压在众人(演员)身上，造成人员受伤。但在实际拍摄中，倒塌的高墙并不会伤害演员，砌成这种高墙的物块最有可能是（）

a、b、c、d是匀强电场中的四个点，它们正好是一个平行四边形的四个顶点，电场线与平行四边形所在平面平行。已知a点的电势为20v，b点的电势为24v，d点的电势为12v，如图所示。由此可知c点的电势为(      )

    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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基因工程是将目的基因通过一定过程，转入到受体细胞中，经过受体细胞的分裂，使目的基因的遗传信息扩大，再进行表达，从而培养出工程生物或生产基因产品的技术。你认为支持基因工程技术的理论有（  ）
①遗传密码具有通用性　        ②基因可独立表达
③基因表达互相影响　         ④DNA作为遗传物质能够严格地自我复制

负鼠(如图)遇到敌害时，就躺下来装死，四脚朝天，两眼直瞪，嘴巴半露，龇牙咧嘴，活像一具僵尸，猛兽看到是一具死尸，掉头就走了。这体现了生物具有哪种特征？(  )