已知梯形的周长，下底和两条腰，则上底等于（ ）。

IV: 任务型读写
请认真阅读下列短文，并根据所读内容在文章后表格中的空格里填入最恰当的单词。注意：每空格1个单词。
One of the roles of the International Olympic Committee (IOC) is to choose the host city for the Olympic Games. The host city election takes place in a country which does not have a candidate city for the Olympics in question. Except for unusual circumstances, the election is held seven years before the Olympic Games take place. There have been two phases leading to the election of the host city since December 1999.
Phase 1: applicant cities
Any city that wishes to host the Olympic Games must be proposed to the IOC by its National Olympic Committee (NOC), with a letter from the city itself. During the first phase, which lasts around ten months, each applicant city must answer a questionnaire to provide general information about itself. Then the applications will be examined carefully. A number of things will be considered, such as government support, public opinion, general infrastructure（基础设施）, safety, accommodations and transport. The IOC Executive Board（执行董事会）will determine which applicant cities will be accepted as candidate cities. Only candidate cities can continue with the procedure.    
Phase 2: candidate cities   
Candidate cities must provide a candidature（候选资格）file according to the instructions given by the IOC. After all the files are examined and the IOC Evaluation Commission（评估委员会）produces its report, the IOC Executive Board draws up a list of final candidate cities. The general assembly of the IOC then takes a vote on the host city.

Choosing the host city of the Olympics
Place	The host city election is (56) _________ in a country that does not apply to be the host city of the Olympics in question.
(57)______	The election takes place seven years (58) ________ the Olympic Games.
Procedure	Phase 1	Participant	Any city that wants to be the (59) _________ of the Olympic Games can be an applicant.
		Process	All cities involved should first ask the NOC to propose them to the IOC; then they need to (60) ________ a questionnaire about themselves.
		Result	The IOC Executive Board (61) ________ the candidate cities.
	Phase 2	Participant	The (62)_________ cities
		Process	The cities have to (63) ________ a file confirming themselves as the candidates. The file should be    (64) _________ on the instructions given by the IOC.
		Result	The IOC Executive Board chooses several cities from the candidate cities. The general assembly of the IOC then (65) _______ for the host city.