题海网,海量题库;找题库、找试卷、找答案就上题海网。

在一个密闭的容器里,用含有同位素14C的脱氧核苷酸合成一个DNA分子,然后加入普通的含12C的脱氧核苷酸,经n次复制后,所得DNA分子中含12C的多脱氧核苷酸链数与含14C的多脱氧核苷酸链数之比是(    )
A . 2n:1 B . (2n-2):n C . (2n-2):2 D . (2n-1):1
生活中难免遇到意外情况,学好生物学知识,可以帮助我们科学应对。以下应对突发意外的措施,不合理的是(  )
A . 静脉血管出血时按压伤口近心端止血 B . 发现有人煤气中毒时,应立即打开门窗,并拨打120急救电话 C . 发现有人触电昏迷时,应立即切断电源 D . 发现有人溺水时,应立即向周边路人呼救,不能轻易下水
⑴⑵⑶阅读短文,判断正误;⑷⑸⑹阅读短文,选择最佳答案。

    When you are in the UK, you must be careful in the streets because the traffic drives on the left. Before you cross a street, you must look to the right first and then to the left. In the morning and in the evening when people go or come home from work, the streets are very busy. Traffic is the most dangerous then.

    When you go by bus in the UK, you have to be careful, too. Always remember the traffic moves on the left, so you must be careful. Have a look first, or you will go to the wrong way.

    In many cities of the UK, there are big buses with two floors. You can sit on the second floor. From there you can see the city very well. It's interesting.

  1. (1) The traffic drives on the left in the UK.
  2. (2) Traffic is the most dangerous in the afternoon.
  3. (3) In many cities of the UK, there are big buses with three floors.
  4. (4) In the UK, the traffic drives ________.
    A . on the left B . on the right C . in the middle
  5. (5) When you cross a street, you must look to ________ first.
    A . the front B . the right C . the left
  6. (6) The Streets become very busy in the morning and in the evening because ________.
    A . people go to work B . people come back from work C . Both A and B
一个质量为m的小铁块沿半径为R的固定半圆轨道上端边缘由静止下滑,当滑到半球底部时,半圆轨道底部所受压力为铁块重力的1.8倍,则此下滑过程中铁块损失的机械能为(   )

图片_x0020_827489762

A . 0.2mgR B . 0.4mgR C . 0.6mgR D . 0.8mgR
Joe Brown had a shop. He sold(卖) meat in his shop . One Thursday a woman came into his shop at five to one . “I’m sorry I’m late,” she said. “I need some more meat for my dinner tonight.” Joe had only one piece of meat in his shop. He took it out of the fridge and said, “This is$6.50.” “That piece is too small.” the woman said, “haven’t you for anything bigger?” Joe went into the room behind his shop, put the piece of meat into the fridge, took it out again and closed the door with lots of noise. Then he brought the piece of meat to the woman and said, “This piece of meat is bigger and more expensive. It's $8.75.” “Good,” the woman said with a smile,“give me both of them.”

  1. (1) Joe Brown was_______________.

    A . a waiter  B . a runner  C . an actor D . a shopkeeper
  2. (2) When did the woman come to Joe's shop?

    A . Early in the morning.  B . Early in the afternoon. C . Late in the morning.   D . At about one o’clock at night.
  3. (3) Why didn’t the woman want that piece of meat?

    A . Because she had no money.     B . Because it was bad. C . Because it wasn’t big enough.   D . Because it was too big.
  4. (4) How many pieces of meat were kept in the fridge?

    A . Only one piece of meat.  B . Two pieces of meat. C . Several pieces of meat.  D . Many pieces of meat.
  5. (5) Could Joe give the woman both pieces of meat?

    A . Of course not.   B . Certainly.     C . He would try his best.  D . Yes, he could.
Don't worry. I'll give this book to Jack as soon as he          back.


A . will come B . has come C . comes D . came
夏季是细菌性痢疾的多发季节,为预防该传染病的发生与流行,防疫部门严禁学校食堂二次销售部分剩余饭菜.该传染病的类型和防疫部门要求的防护措施分别属于(   )
A . 消化道传染病    切断传播途径 B . 呼吸道传染病    控制传染源 C . 消化道传染病    保护易感人群 D . 消化道传染病    控制传染源

如图,在平行六面体ABCD—A1B1C1D1中,M为AC与BD的交点.若=a=b=c , 则下列向量中与相等的向量是(   )

A .  a + b +c B .  a + b +c C .  a  b +c D .  a  b +c
2022年5月12日是我国第十四个全国防灾减灾日,面对灾害和意外,下列措施不合理的是(   )
A . 泥石流发生时,应设法从房屋里跑出并顺沟方向往上游或下游逃生 B . 发生火灾且室内浓烟密布时,应俯伏在地上爬行并用潮湿毛巾掩盖口鼻 C . 发生地震时,底楼的人应迅速跑到室外开阔的地带避险 D . 发现煤气中毒者,首先必须将病人从中毒环境迅速转移到空气清新的地方
关于甲、乙两地地理位置的描述,正确的是(  )

A . 甲地位于南美洲最南端,西临印度洋 B . 甲地位于非洲最南端,西临大西洋 C . 乙地位于北美洲东部,东临太平洋 D . 乙地位于亚洲东部,东临大西洋
We can make the cookies by (we).
如图1,在矩形ABCD中, , 把AB绕点B顺时针旋转得到,连接,过B点作于E点,交矩形ABCD边于F点.

  1. (1) 求DA′的最小值;
  2. (2) 若A点所经过的路径长为 , 求点A′到直线AD的距离;
  3. (3) 如图2,若 , 求的值;
  4. (4) 当的度数取最大值时,直接写出CF的长.
流行性感冒的传染源是(    )

A . 流感患者 B . 空气和飞沫 C . 老人和小孩 D . 流感病毒
下图示意中国、日本、意大利和法国四个国家的城市化率变化情况,曲线上的圆点表示各国不同高铁线路开始营运的时间。据此完成下面小题。

  1. (1) 关于图中四国高铁运营与城市化的描述,正确的是(   )
    A . 甲国城市化水平高,高铁开始运营时间最早 B . 1995~2005年,乙国新增高铁运营线路最多、城市化速度最快 C . 丙国高铁开始运营时间最早,城市化水平最高 D . 2000~2010年,丁国高铁新增运营线路最多,城市化速度最快
  2. (2) 与甲、乙、丙三国相比,丁国(    )
    A . 城市化水平高 B . 城市人口数量最多 C . 城市化起步早 D . 出现逆城市化现象
2022年北京冬奥会自由式滑雪项目上,中国选手“天才少女”谷爱凌获得了金牌。下列有关叙述错误的是(  )
A . 滑雪运动是学习行为 B . 滑雪受神经系统和激素的调节 C . 骨骼肌受到刺激有收缩的特性 D . 运动系统是由骨和骨骼肌构成的
春天来了,杨柳吐絮,百花争艳,让人眼花缭乱。但如果我们把这些植物进行科学分类,就可以弄清它们之间的亲缘关系以及相似程度。下图为植物分类系统图解,请回答下列问题:

图片_x0020_22999483

  1. (1) 对被子植物进行分类时,往往把种子、花和作为分类的重要依据。
  2. (2) 图表的分类等级中,包含生物种类最多的是,多种多样的生物体现了生物种类多样性,而生物种类多样性的实质是
  3. (3) 图表的植物中,与玫瑰的亲缘关系最近,共同特征最多,它们共有的分类单位从大到小的顺序为界、门、纲、目、科、属、
  4. (4) 对生物进行分类的意义在于可以弄清它们之间的亲缘关系和关系。
龙舟赛上,运动员手持船桨奋力向后划水,龙舟向前运动,这是因为物体间力的作用是的;比赛时,并排前进的龙舟不能离得太近,是由于两龙舟间水的流速越大,压强越,容易相撞。

在提到某一条约时说:“(它)巩固了两国的友好关系,一方面使我们能够放手地和较快地进行国内的建设工作,一方面叉正在推动着全世界人民争取和平和民主反对战争和压迫的伟大斗争。”该条约是(   )
A . 《日内瓦公约》 B . 《中美友好通商航海条约》 C . 《朝鲜战争协定》 D . 《中苏友好同盟互助条约》
—What did you do there?

—I .

P(-2,-3)向左平移1个单位,再向上平移3个单位,则所得到的点的坐标为(  )
A . (-3,0) B . (-1,6) C . (-3,-6) D . (-1,0)
教材章节知识点
年级分类
最近更新