a helicopter can be defined as any flying machine using rotating wings to provide lift,propulsion,and control forces that enable the aircraft to hover relative to the ground without forward flight speed to generate these forces.
爱着你,就要让全世界都知道你的好!——致中国大学MOOC
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2015年我大学毕业十年,同学们重回校园聚会,感慨万千,还是怀念学生时代。又讲起当年的四大名捕课程,挂科的, […]
7 years ago
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