单选题A square countertop has a square tile inlay in the center, leaving an untiled strip of uniform width around the tile. If the ratio of the tiled area to the untiled area is 25 to 39, which of the following could be the width, in inches, of tile strip? Ⅰ.1 Ⅱ.3 Ⅲ.4

单选题在等比数列an)中，已知Sn=36，S2n=54，则S3n=( )．

单选题设有直线，则该直线必定______A.过原点，且垂直于x轴B.过原点，且平行于x轴C.不过原点，且垂直于x轴D.不过原点，且平行于x轴

单选题甲单独15天完成某项工作，乙单独做10天可完成这项工作，结果是甲先做了12天后再由乙接下去做，要完成该项工作还需做( )．

单选题某车间接到一批任务，需要加工6000个A型零件和2000个B型零件，车间共有224名工人，每人加工5个A型零件所用的时间可以加工3个B型零件，将这批工人分成两组，两组同时工作，每组加工一种型号零件，为了在最短时间内完成任务，应分配来加工B型零件的人数为______

单选题设，f(x)=ln(1+x2)，则=______。A.-6B.-6ln2C.6ln2D.6

单选题One thing that Ismael Matos, 23, says he's learned on his job as a special agent with the Geek Squad, is that there are no stupid questions—not even when a customer asks where the power button is. The goal, Matos says, is first to "strip out the jargon. " You know what he means: those terms like gigs, Ram, and motherboard that civilians don't typically use in everyday conversations. Once he establishes a common language with the customer, Matos can focus on building a relationshipone that he hopes will pay off in the future. Matos knows that clients often don't have the same skills he does. His customers ask for help not only with setting up new computers and installing software, but also with digital cameras, wireless Internet access and even getting their iPod synced with iTunes. We live in the age of Web2.0, when Internet viewers are fast becoming content creators. We may log in to social networking sites such as Digg and Technorati, rate or even upload videos on YouTube, and contribute and edit information on collaborate websites known as wikis. But members of this expanding plugged-in population aren't necessarily up to speed with the language of the web—or understand the technical lingo of the sales or customer service people they're turning to for assistance. According to a "Cyber Stress" survey of 1,001 American broadband Internet service users, 46 percent said the typical tech support person uses an excess of technical language, and 61 percent said they would prefer a "computer therapist" who is compassionate and easy to talk to. A question that online public relations strategist Sally Falkow says she's hearing often these days is, "How do we cope with all this?" she tells people, "There's no way you can escape this. There's a big conversation going on," and it's important to learn how to be part of it. If you're at the earliest stage of the learning curve, start by reading technology-oriented columns and articles in magazines, newspapers and websites that are written for a general audience. Move up to more tech-oriented e-letters as you build a foundation. As you come across new tells, look them up online. Definitions at Wikipedia, the online encyclopedia written and edited by web users, may be helpful. You should also start associating with people who can help explain things. Look for groups that sponsor seminars or find a supportive online community. Don't be afraid to guide your helper. Explain what you need to know, ask him or her to slow down and speak in basic terms.

单选题设曲线y=x-ex在点(0，-1)处与直线l相切，则直线l的斜率为______． A.∞ B.1 C.0 D.-1

单选题设总体X服从标准正态分布，(X1，X2，…，Xn)为总体的简单样本

单选题若实数a，b满足则ab=______．

单选题在区间[0，+∞)内，方程______．