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______．

单选题某次乒乓球单打比赛中，先将8名选手等分为2组进行小组单循环赛．若一位选手只打了1场比赛后因故退赛，则小组赛的实际比赛场数是______．

单选题设函数f(x)具有2阶导数，g(x)=f(0)(1-x)+f(1)x，则在区间[0，1]上 A.当f'(x)≥0时，f(x)≥g(x)． B.当f'(x)≥0时，f(x)≤g(x)． C.当f"(x)≥0时，f(x)≥g(x)． D.当f"(x)≥0时，f(x)≤g(x)．

单选题与直线2x-4y+4=0的夹角为45°，且与这直线的交点恰好在x轴上的直线方程是（　）

单选题车间共有40人，某次技术操作考核的平均成绩为80分，其中男工平均成绩为83分，女工平均成绩为78分，该车间有女工( )人。

单选题等差数列an)中，a5＜0，a6＞0，且a6＞|a5|，Sn是前n项之和，则( )．

单选题某产品的产量Q与原材料A，B，C的数量x，y，z(单位均为：吨)满足Q=0.05xyz，已知A，B，C每吨的价格分别是3，2，4(百元)．若用5400元购买A，B，C三种原材料，则使产量最大的A，B，C的采购量分别为______．

单选题李先生从家到单位驾车到单位要经过4个有红绿灯的路口，假设在各路口是否遇到红灯是相互独立的，且遇到红灯的概率都是，遇到红灯时停留的时间都是2分钟，则李先生从家到单位的路上因遇到红灯停留的总时间至多是4分钟的概率为()．

单选题直线

单选题方程|x-|2x+1||=4的根是( )．

单选题Agroupof20friendsformedaninvestmentclub,witheachmembercontributinganequalamounttothegeneralfund.Theclubtheninvestedtheentirefund,whichamountedtoddollars,inStockX.Thevalueofthestocksubsequentlyincreased40percent,atwhichpointthestockwassoldandtheproceedsdividedevenlyamongthemembers.Intermsofd,howmuchmoneydideachmemberoftheclubreceivefromthesales(Assumethattransactionfeesandotherassociatedcostswerenegligible).