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For the first time, a woman captain led Britain’s Changing of the Guard ceremony at Buckingham Palace. Canadian officer Megan Couto made history on June 26 by commanding the troops guarding Queen Elizabeth's London home. Couto, 24, led her Canadian unit in the ceremony, which is witnessed by thousands of visitors to London each year. Her unit is the Second Battalion, Princess Patricia's Canadian Light Infantry （步兵），also known as The Patricia's.The British Army said Couto was the first ever female infantry officer to lead the ceremony. “We look forward to seeing a British Army fem开瓶盖的起子可以看作是一个杠杆，在下图中正确表示开瓶盖时该杠杆支点、动点和阻力是: