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______．

单选题已知f(x)的一个原函数为ex2，则为______。A．B．C．D．

单选题 Advertisers tend to think big and perhaps this is why they're always coming in for criticism. Their critics seem to resent them because they have a flair for self-promotion and because they have so much money to threw around. "It's iniquitous," they say, "that this entirely unproductive industry (if we can call it that) should absorb millions of pounds each year. It only goes to show how much profit the big companies arc making. Why don't they stop advertising and reduce the price of their goods? After all, it's the consumer who pays." The poor old consumer. He would have to pay a great deal more if advertising didn't create mass markets for products. It is just because of the heavy advertising that consumer goods are so cheap. But we get the wrong idea if we think the only purpose of advertising is to sell goods. Another equally important function is to inform. A great deal of the knowledge we have about household goods derives large from the advertisements we read. Advertisements introduce us to new products or remind us of the existence of ones we already know about. Supposing you wanted to buy a washing-machine, it is more than likely you would obtain details regarding performance, price, etc. from an advertisement. Lots of people pretend that they never read advertisements, but this claim may be seriously doubted. It is hardly possible not to read advertisements these days. And what fun they often are, too] Just think what a railway station or a newspaper would be like without advertisements. Would you enjoy gazing at a blank wall or reading railway by-laws while waiting for a train? Would you like to read only closely-printed columns of news in your daily paper? A cheerful, witty advertisement makes such a difference to a drab wall or a newspaper full of the daily ration of calamities. We must not forget, either, that advertising makes a positive contribution to our pockets. Newspapers, commercial radio and television companies could not subsist without this source of revenue. The fact that we pay so little for our daily paper, or can enjoy so many broadcast programs is due entirely to the money spent by advertisers. Just think what a newspaper would cost if we had to pay its full price ! Another thing we shouldn't forget is the "little ads", which are in virtually every newspaper and magazine. What a tremendously useful service they perform for the community ! Just about anything can be accomplished through these columns. For example, you can find a job, buy or sell a house, announce a birth, marriage or death in what used to be called the "hatch, match and dispatch" columns; but by far the most fascinating section is the personal or "agony" column. No other item in a newspaper provides such entertaining reading or offers such a deep insight into human nature. It's the best advertisement for advertising there is!

单选题已知ab＜0，bc＜0，则直线ax+by=c通过______

单选题已知6x 2 +7xy-3y 2 -8x+10y+c是两个关于x，y的一次多项式的乘积，则常数c=______．

单选题设，其中A4j为元素a4j(j=1，2，3，4)的代数余子式，那么A41+A42+A43+A44=()。A．0B．1C．6D．3

单选题若=()．

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______

单选题设向量组α1=(1，2，3，4)，α2=(2，3，4，5)，α3=(3，4，5，6)，α4=(4，5，6，7)，则r(α1，α2，α3，α4)=______。 A．2 B．3 C．4 D．5

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()。

单选题已知，那么s的范同是()。

单选题______．

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

单选题如图所示，AC，BP将四边形分为四部分，已知△AOP的面积为6，△AOB的面积为9，则阴影部分面积为______．A．15B．C．D．E．16

单选题f(x)在[0，+∞)上可导，f(0)=0，并有反函数g(x)，若，则f(x)=______。A．(2+x)ex-1B．(2+x)ex+cC．(1+x)ex-1D．(3+x)ex+c

单选题下列结论正确的是______。A．若a为无穷小量，则必为无穷大B．任意两个无穷小量均可以比较阶的大小C．若，且xn为无界数列，则有D．若，且n→∞时，xn为无穷大量，则yn为无穷小量