题目

如图所示，小木块的质量为m，可看成质点，木板质量为M＝2m，长度为l，一根质量不计的轻绳通过定滑轮分别与M和m连接，小木块与木板间以及木板与水平面间的动摩擦因数均为，开始时木块静止在木板左端。现用水平向右的恒力将木块拉至木板右端，则 A．拉力至少为4mg         B．拉力至少为5mg C．拉力至少做功5mgl          D．拉力至少做功2.5mgl                        　　阅读理解：阅读下列短文，从每题所给的四个选项（A、B、C和D）中，选出最佳选项． 　　The Times of London has launched an important new service-E-paper. It's radically (根本的) different from the current on-line service, but exactly the same as the printed newspaper bark in Britain. The News, Sport, Business section, T2, The Game (every Monday), the classified ads, even the crossword are all laid out just as in the paper. It's the actual paper… without the paper. To try a free demonstration, click the button below. 　　Now you can access The Times newspaper as it is printed from 5 am GMT on the day of publication. For the first time, wherever you are outside the UK, you can get today's newspaper on your screen for just 24 pence per day. 　　In addition to the new E-paper, subscribing (订阅) to Times Online gives you the complete Newspaper Edition Headline List, as well as full access to the Times Online website and all associated online services. 　　Your subscription now brings you daily access to: 　　The new E-paper edition 　　The Times Online website and services 　　The Newspaper Edition Headline List 　　You can pay in any one of the following ways: 　　One off monthly subscription: ￡7.50 　　Monthly payment scheme: ￡6.50 per month 　　Annual payment scheme: ￡75.00 per year 1．Where can this ad be found? [　　] A．On a computer.B．In a newspaper. C．On an ad board.D．On TV. 2．The underlined sentence “It's the actual paper.… without the paper” means ________. [　　] A．information in E-paper can be received free of charge B．information in E-paper is given without being printed C．information in E-paper cannot be found in any other papers D．information in E-paper is limited to only a few fields 3．It can be inferred from the advertisement that________. [　　] A．the more papers you subscribe to, the less you will have to pay B．the longer your subscription to the paper is, the less you will have to pay C．the Times newspaper is printed in different parts of the world D．what happen in the late afternoon will appear in the same day's Times