“中国护照的含金量不仅仅在于它能帮你免签去多少个国家和地区，更在于危急时刻来临时，祖国能带你回家！”这是身为中国公民的自豪；也是“外交为民”最好的写照。2015年以来，中国政府继续秉承以人为本、外交保护为民的理念，持续推进海外民生工程，保护中国在海外机构和公民的安全和正当权益，为“中国脚步”走出国门保驾护航。中国全力保护海外公民安全是因为(         )

①民主是专政的前提和基础  

②我国人民民主具有真实性

③公民的国家意识和民主意识不断增强

④人民民主专政的本质是人民当家做主

如图所示，在竖直平面内半径为R的四分之一圆弧轨道AB、水平轨道BC与斜面CD平滑连接在一起，斜面足够长．在圆弧轨道上静止着N个半径为r（r＜＜R）的光滑刚性小球，小球恰好将圆弧轨道铺满，从最高点A到最低点B依次标记为1、2、3…N．现将圆弧轨道末端B处的阻挡物拿走，N个小球由静止开始沿轨道运动，不计摩擦与空气阻力，下列说法正确的是（　　）

    Two farmers were on their way home one evening after a hard day's work．Both were tired．They happened to look up at the sky and saw a black cloud overhead．
    "Ah!" said one farmer, "tomorrow we shall have rain and the rice will grow well．" The second answered, "Nonsense （胡说）, the rain will only kill the crops （庄稼）．"
    So they began to fight．Just then a third farmer came along and asked them why they were quarreling（争吵）．Both farmers explained about the black cloud．
    "What cloud?" asked the third farmer．They all looked at the sky．The cloud was no longer there．