题目

阅读理解Rome wasn't built in a day, and the Internet didn't come out of a golden egg. Many of today's creations were not born of people who had creative ideas, but who did not stop at simply having an idea. They took one brick of capital (资本), another brick of knowledge, perhaps a brick or two of family and friends, and built their empires (帝国) brick by brick.If you want to build an online empire, you cannot settle for simply having a website full of articles, or a website full of pictures?there are already thousands of sites like that, so you need to come up with something new and利用如图所示装置将重为100N的物体匀速从斜面的底端拉到顶端．已知斜面的长是5m，高是2m，拉力为F=50N，则该装置的机械效率为（ ）A．40%B．50%C．80%D．100%