某地区中小学人数的分布如下表所示：学段城市县镇农村小学2000001500001 发布时间：2017-05-03 13:33 │ 来源：www.tikuol.com 题型：填空题 问题： 某地区中小学人数的分布如下表所示：学段城市县镇农村小学200000150000180000初中17000011000050000高中800002000010000若要从中抽取一个容量为总体容量的千分之一的样本，则合适的抽样方法是______，城市高中、县镇初中、农村小学抽取的人数分别是______、______、______．
题型：填空题 下列叙述正确的是[ ]A．检验生物组织中的糖类、脂肪和蛋白质实验时可用有颜色的材料作为实验材料 B．鉴定生物组织中的还原糖时加入的斐林试剂要先加甲液后加乙液 C．观察DNA和RNA在细胞中的分布实验中盐酸的作用能改变细胞壁的通透性 D．用显微镜观察线粒体实验，健那绿可使线粒体呈现蓝绿色 查看答案
题型：填空题 某同学在上学的路上，测得自己前一半时间内的平均速度为4m/s，后一半时间内的平均速度为6m/s．①试求他在全程中的平均速度是多少？②假如他在前一半路程中的平均速度为V1，后一半路程中的平均速度为V2，试推导：他在全程中的平均速度为V=2V1V2V1+V2． 查看答案
题型：填空题 Directions: There are 10 blanks in the following passage. For each numbered blank, there are 4 choices marked A, B, C and D. The key to the industrialization of space is the U.S. space shuttle. (51) it, astronauts will acquire a workhouse vehicle (52) of flying into space and returning many times. (53) by reusable rockets that can lift a load of 65 000 pounds, the shuttle will carry devices for scientific inquiry, as well as a variety of military hardware. (54) more significantly, it will deliver materials and machines into space for industrial purposes (55) two decades ago when "sputnik" (artificial satellite) was added to the vocabulary. In short, the (56) importance of the shuttle lies in its promise as an economic tool. What makes the space shuttle (57) is that it takes off like a rocket but lands like an air plane. (58) when it has accomplished its mission, it can be ready for (59) trip in about two weeks. The space shuttle, the world’s first true spaceship, is a magnificent step (60) making the impossible possible for the benefit and survival of man.A．ThusB．WhereasC．NeverthelessD．Yet 查看答案