题目

The Red Cross turned the school into a _______ for victims of the earthquake. A. kindergarten             B. cover                       C. shelter                      D. hotel 答案：C 作图 如下所示，使用羊角锤拔钉子，动力作用在锤柄上A点，请作出拔钉子时所用最小动力F的示意图．