When most people think pencils, the No. 2 pencil is the first thing that comes to mind. But what does the “2” on a No. 2 pencil actually mean? And what do all of the “B’s,”“H’s” and “HB’s” being thrown around mean, for that matter? Well, it a
2001年末，全国共有艺术表演团体2622个，文化馆2911个，公共图书馆2769个，博物馆1373个，档案馆3816个；共出版全国性和省级报纸203亿份，各类杂志 28.5亿册，图书63.5亿册；共有中、短波广播发射台和转播台1313座，电视综合人口覆盖率93.4%；全国有线电视用户7920万户，成为世界上有线电视用户最多的国家...
(5分)在t=0s时刻向平静水面的O处投下一块石头，水面波向东西南北各个方向传播开去，当t=1s时水面波向西刚刚只传到M点（图中只画了东西方向，南北方向没画出），OM的距离为1m,振动的最低点N距原水平面15cm, 如图，则以下分析正确的是 (填正确答案标号。选对1个得2分，选对2个得4分.选对3...