题目

A、B、C三个阀门，同时开放，1小时可注满水池．只开放A、C两个阀门，1.5小时可注满水池．只开放B、C两个阀门，2小时可注满水池．问：只开放A、B两个阀门，需多少时间才能注满水池? 答案：解：设单独开放A、B、C三个阀门，分别需x、y、z小时才能注满水池．由题意，得{1x+1y+1z=1①32(1x+1z)=1②2(1y+1z)=1③将 1x、1y、1z 视为整体，解得 1x=12，1y=13、1z=16所以 1x+1y=56 ④即只开放A、B两个阀门，注满水池需1÷56=65 （时）答：需 65 小时阅读理解Apply for a Library CardAny person who lives, works or attends school in New York State is qualified to receive a New York Public Library card free of charge.Adult and teen users may either apply online or in person at any New York Public Library location. Applications for children aged 11 and under must be completed in person, and require the signature of a parent or guardian.When you apply for a card online, you will receive a 7-digit temporary barcode(条形码). This allows you to set a PIN (Personal Identification Number).After you receive your permanent barcode, which is required to borrow materials, search library databases, or reserve a computer, you must validate your card.Renew or Validate Your CardAll adult, teen and child library cards for cardholders in New York City and areas of New York State outside of New York City expire(期满) and must be renewed every three years. New library card applicants who applied for a card online must validate their card before full cardholder privileges can be extended.Cardholders in New York City must visit any New York Public Library location to present the required forms of identification in order to renew or validate their card.Cardholders from areas of New York State outside of New York City may email scans or copies of the required forms of identification to patronaccounts@nypl.org.Forgot Your PIN?If you provide the library with a valid email address, you can click on the Forgot Your PIN? Link on the login(登录) screen of either Biblicisms or the Classic Catalog. A link with instructions on changing your PIN will be sent to the email address on your account, giving you a brief period of time to update your information. You must select a 4-digit numeric PIN, with no repeating or obvious characters(e.g.1234 or 2222).If you have not provided us with a valid email address, you have to visit a library location with valid identification to have a staff member reset your PIN for you.（1）If a 10-year-old boy wants to receive a New York Public Library card, he ___________.A.can either apply online or in personB.can ask his parents to apply for himC.has to visit a library location in personD.has to apply in person with a parent or guardian（2）Which is different for cardholders in New York City and those from areas of New York State outside of New York City?A.The full cardholder privileges.B.The way they renew or validate their card.C.The period of validity of their card.D.The way they apply for a card.（3）A cardholder who forgot his PIN and didn't provide the library with a valid email address ____________.A.can reset his PIN by letterB.has to apply for an email addressC.can call the library to reset his PIND.has to go to the library to have his PIN reset（4）What is the best title of the passage?A.How to apply for a Library Card.B.The way people renew their card.C.The time people can keep the card.D.The money people have to pay for a card.