单选题若用浓度为30%和20%的甲、乙两种食盐溶液配成浓度为24%的食盐溶液500克，则甲、乙两种溶液各取______．

单选题直线y=x+k与曲线恰有一个公共点，则k的取值范围是______

单选题一列客车长250m，一列货车长350m，在平行的轨道上相向行驶，从两车头相遇到两车尾相离经过15s，已知客车与货车的速度之比是5:3。问两车的速度相差______。

单选题函数y=4x的图像与直线y=4的交点坐标为

单选题In promising to fuse media as diverse as television, telephone communication, video games, music and data transmission, the era of digital convergence goes better than yesterday's celebrated "information superhighway". Yet achieving this single technology is far from straightforward. There are currently three major television broadcast standards, and they are all incompatible with each other. But this is nothing compared to the many technologies supporting the Internet, each with a different bandwidth and physical media. The problems faced in designing platforms and communication systems that will be accepted across the world can appear insuperable. Even once global standards are assured, however, a further obstacle lies in wait. The Internet is plagued by long, erratic response times because it is a pull-technology, driven by patterns of user demands. Push technology, on the other hand, reverses the relationship: servers simply send information to passive users, as in television and radio. But if some form of combination between one-way television flow and interactive Internet is to be the basis of our future media, it is hard to see how it could be operated. Moreover, the problem of fusing Internet with television is also one of defining the services offered. Information, entertainment and relaxation appear at first to be quite different needs. Serious doubts remain over whether consumers will be interested in having to make the sort of mental effort associated with computing while also settling down in front of a sitcom. Besides the issue of consumer habits, infrastructure costs are set to be immense, and will have to be met by national states or the private sector before being passed on to users. Platforms do not necessarily have to be expensive. The mobile phone is a good example of how something that is technologically sophisticated can almost be given away, with its cost recovered through service charges. Users are then coerced through clever marketing to upgrade to newer phones with more features to reinforce their dependence. Whatever the outcome, it is obvious that technology will play an increasing part in our everyday lives. Beyond technology, digital convergence embraces the services, industrial practices and social behavior that form modern society. We have in our hands the technology to construct the most sophisticated machines ever built, but if they are unusable, simply because of their operating instructions, then recent lessons have taught us they will not survive. Whatever we design must be simple, reliable and useful. Perhaps this is where artificial intelligence will come in.

单选题______．A．1B．0C．D．

单选题甲、乙、丙三人独立向目标射击，击中目标的概率分别为．现在他们同时开枪向目标射击一次，则恰有两发子弹击中目标的概率是()．

单选题下列函数中____在点x=0处可导。A．B．e-xC．|x|D．|sinx|

单选题公司有职工50人，理论知识考核平均成绩为81分，按成绩将公司职工分为优秀与非优秀两类，优秀职工的平均成绩为90分，非优秀职工的平均成绩是75分，则非优秀职工的人数为______．

单选题铁路旁的一条平行小路上，有一行人与一骑车人同时向南行进。行人速度为3.6km/h，骑车人速度为10.8km/h。这时有一列火车从他们背后开过来，火车通过行人用22s，通过骑车人用26s。这列火车的车身总长是______m。

单选题设，则下列向量是A的特征向量的是

单选题More surprising, perhaps, than the current difficulties of traditional marriage is the fact that marriage itself is alive and thriving. As Skolnick notes, Americans are a marrying people: Relative to Europeans, more of us marry and we marry at a younger age. Moreover, aster a decline in the early 1970s, the rate of marriage in the United States is now increasing. Even the divorce rate needs to be taken in this pro-marriage context: some 80 percent of divorced individuals remarry. Thus, marriage remains, by far, the preferred way of life for the vast majority of people in our society. What has changed more than marriage is the nuclear family. Twenty-five years ago, the typical American family consisted of a husband, a wife, and two or three children. Now, there are many marriages in which couples have decided not to have any children. And there are many marriages where at least some of the children are from the wife's previous marriage, or the husband's, or both. Sometimes these children spend all of their time with one parent from the former marriage; sometimes they are shared between the two former spouses. Thus, one can find the very type of family arrangement. There are marriages without children; marriages with children from only the present marriage; marriages with "full-time" children from the present marriage and "part-time" children from former marriages. There are step-fathers, step-mothers, half-brothers, and half-sisters. It is not all that unusual for a child to have four parents and eight grandparents! These are enormous changes from the traditional nuclear family. But even so, even in the midst of all this, there remains one constant: Most Americans spend most of their adult lives married.

单选题一批救灾物资分别随16列货车从甲站紧急调到600公里外的乙站，每列车的平均速度为125公里/小时．若两列相邻的货车在运行中的间隔不得小于25公里，则这批物资全部到达乙站最少需要的小时数为______．

单选题当今世界的主题是______。 A．和平与发展 B．战争与革命 C．民主与人权 D．改革与开放

单选题设a＜b＜c＜d，如果x=(a+b)(c+d)，y=(a+c)(b+d)，z=(a+d)(b+c)，那么x，y，z的大小关系为______

单选题若且sinθ＜0，则θ所在象限为{{U}}{{/U}}．A.第一象限B.第二象限C.第三象限D.第四象限

单选题中国对外政策的根本原则是______。 A．和平共处五项原则 B．独立自主 C．反对霸权主义、强权政治 D．维护世界和平，促进人类共同繁荣和发展

单选题设在(-∞，+∞)内连续，且，则______．

单选题设，利用等差数列前n项和公式，求得f(-5)+f(-4)+…+f(0)+…+f(5)+f(6)的值为()。

单选题某人以6公里/小时的平均速度上山，上山后立即以12公里/小时的平均速度原路返回，那么此人在往返过程中每小时平均所走的公里数为______．