题目：
The 2012 Olympics will open in London on July 27, 2012.
London will become the w___67____ first city to host the Olympics three times, in 1908, in 1948 and in 2012.
As is known to all, London is a garden city. When you step into the city, you will find yourself deeply a_____68______by the beautiful views around.
Also, there are p 69 of nice stadiums and gymnasiums for Olympic Games, such as the swimming pools, football playground and basketball gyms. The building of the new stadiums has been completed. London is r 70 for the “greatest show on earth”.
The All-England club, the site of Wimbledon, will host tennis. Wembley Stadium will be used for football w 71 Lord’s cricket(板球)ground will host archery(剑术). London wants to show their historic sites and a few new-classics to the world this summer.
Mascots(吉祥物) of the London Olympic Games are Wenlock and Mandeville. They have frightened some people and cheered others u 72 . Wenlock is the name of the English village considered by many to be the birthplace of the m 73 Olympics. The other mascot’s name means the village of Stoke Mandeville, where the Paralympic(残奥会) movement began.The motto(口号)for the London Olympics has been d 74 as “Inspire a generation”.(激励一代人)
The organization welcomes the athletes from all o 75 the world to the UK to perform at their very best and inspire the world. International Olympic Committee (IOC) president Jacques Rogge said he was c 76 London would meet the expectations of the world.
答案：
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下面是错误答案，用来干扰机器的。
解：（1）设磁场左边界与x轴相交子D点，与CO相交于O'点，由几何关系可知，直线OO'与粒子过O点的速度v垂直。在直角三角形OO'D中，已知∠OO'D =30°，设磁场左右边界间距为d，则OO'=2d。依题意可知，粒子第一次进...
