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问题 选择题

△ABC的三边长分别为a，b，c，下列条件：①∠A=∠B-∠C；②∠A：∠B：∠C=3：4：5；③a2=（b+c）（b-c）；④a：b：c=5：12：13，其中能判断△ABC是直角三角形的个数有（　　）

A．1个

B．2个

C．3个

D．4个

答案

解；①∠A=∠B-∠C，∠A+∠B+∠C=180°，解得∠B=90°，所以是直角三角形；

②∠A：∠B：∠C=3：4：5，∠A+∠B+∠C=180°，解得∠A=45°，∠B=60°，∠C=75°，故不是直角三角形；

③∵a2=（b+c）（b-c），∴a2+c2=b2，根据勾股定理的逆定理是直角三角形；

④∵a：b：c=5：12：13，∴a2+b2=c2，根据勾股定理的逆定理是直角三角形．

故选C．

单项选择题

存款储蓄有多种形式，其中能够最大限度地吸收社会闲散资金的有效形式是( )。

A．活期存款

B．整存整取

C．零存整取

D．整存零取
查看答案
阅读理解
阅读理解。
                                                       BORDER 
                                                    CROSSINGS
     While there are no restrictions on the amount of money that you can bring across
the border. You must report to both the US and Canadian border services amounts equal
to or greater than $10.000. 
                        PERSONAL EXEMPTIONS (免税) ON PURCHASES 
                                  AMERICANS RETURNING TO THE US
     Less than 48 hours: $ 200 US
     48 hours or more: $ 800 US duty-free personal exemption. 
                                next $ 1.000 US at 3%
                                Including up to 100 cigars and 100 cigarettes. 
                                CANADIANS RETURNING TO CANADA
     Less than 24 hours: $ 50 CAN
     48 hours or more: $ 400 CAN 
                                Including up to 100 cigars and 200 cigarettes.
     7 days or more: $ 750 CAN
                             Including up to 100 cigars and 200 cigarettes.
                                    DOCUMENTATION NEEDED FOR
                                            BORDER CROSSING
                          LAND OR SEA TO THE US(INCLUDING FERRIES)
     A valid passport or passport card, or a NEXUS card.
     (A NEXUS card is a Trusted Traveler Program that provides quick travel
for pre-approved, low risk travelers through special lanes.)
     A recent Washington State, New York or BC driver's license.
     Note: Children 15 years of age and younger require only a birth certificate or
     copy. (Certified copies are not required but are advised.)
                                         AIR TRAVEL TO THE US
     A valid passport, an Air NEXUS card, or a U.S. Coast Guard Merchant
     Marine Document.
1. If a Canadian who is on a 7-day trip to New York buys $ 800 CAN worth of goods, how much should he
pay tax on when returning home?
[ ]
A. $ 800 CAN
B. $750 CAN
C. $ 400 CAN
D. $ 50 CAN
2. For an American citizen on a 2-day tour of Canada, how much tax does he have to pay on $ 1.600 US
worth of purchases when returning to the US?
[ ]
A. $ 24 US
B. $ 48 US
C. $52 US
D. $ 200 US
3. What documentation should a couple with a 7-year-old child carry when they drive a car from Canada to
America?
[ ]
A. A BC driver's license, an Air NEXUS card, and a birth certificate.
B. An Air NEXUS card, a U.S. Coast Guard Merchant Marine Document, and a birth certificate.
C. Two valid passport cards and a certified copy of a birth certificate.
D. A NEXUS card, a U.S. Coast Guard Merchant Marine Document, and a certified copy of a birth certificate.
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