题目内容
二阶系统阻尼比=1时，系统有两个不等的负实根（）。
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一阶系统阶跃信号作用下的调节时间随着时间常数T的增大而增大（）。
一阶系统的阶跃响应没有超调量（）。
What is the main point of the report?
Lester Holt: This is NBC Nightly News with Lester Holt. Good evening from Los Angeles. As we welcome our Viewers of the West, France has been rocked again by an act of terror. After a period of relative quiet and ISIS defeats, a lone attacks reportedly calling himself a soldier of the Islamic State went on ta bloody shooting in southern France today before being corncerned in a supermarket with hostages. Tonight, outside Paris, a minute of silence as 80,000 soccer fans in France's national stadium honor the three people killed and 16 wounded in the attack. A that might have been considerably higher if not for an incredibly brave act by a police officer. Our chief foreign correspondent Richard Engel has details.Richard Engels: It's a scene France and the world know too well. A lone attacker pledging to ISIS unleashing terror. This time holding hostages in this supermarket. Police identified him as Redouane Lakdim, a small-time drug dealer, police say, seen walking his younger sister to school before the shooting spree. At 10:13 am, Lakdim a car, killing a passeger. Before 11:00, he drives past a group of police officers, opening fire, injuring one of the officers. Minutes later, Lakdim arrives at the supermarket. "I saw a person very with a handgun in one hand and a knife in the other shouting 'Allahu Akbar'",says a man who helped other shoppers hide in a meat locker. The dramatic ending after the heroic actions of a police officer identified as Arnaud Beltrametrading places with hostages, smartly leaving his phone on, so officers outside can listen in. SWAT teams enter when they hear gunshots. Beltrame is seriously injured, the suspect is killed. France has been a for ISIS violence from an Islamic radical killing four in a kosher grocery store to attacks on a concert in a stadium in Paris. Tonight, authorities the gunman's apartment and praising the actions of one brave officer who may have saved many lives. Richard Engel, NBC News.
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