题目

Principles of Effective Public SpeakingWhen we watch politicians, or business leaders speak on television or in public, they seem so at ease that we may wonder: are great speakers made, or are they just born that way? While it is true that some individuals are born with this gift, many effective public speakers have trained themselves to be so. 【1】Here are some principles of public speaking that I’ve developed in my role as a media coach.Stop trying to be a great “public” speaker. People want to listen to someone who is interesting, relaxed, and comfortable. In the routine conversati一质量为m的木块静止在光滑的水平地面上，从t=0开始，将一个大小为F的水平恒力作用在该木块上，在t=t1时刻力F的功率是（     ） A．B．C．D．