如图所示，矗立在天安门广场的人民英雄纪念碑，碑身高37.94m，由423块花岗岩石块砌成，碑心石是一块竖立的整块花岗岩，高14.7m、宽2.9m、厚1.0m、质量119.3t，求：

①碑心石体积；

②碑心石密度；

③若碑心石单独静止竖立于水平地面上，它对水平地面的压强．

Every child has his own dream．Every child hopes to be an adult．However, is it truly like what they imagine? As a boy who lives in modem times and in a modern city，I feel greater pressure on me with the city’s development．Although we seldom worry about money, we still have a lot of others such as competitions among classmates and expectations from parents．These experiences are very helpful to our future．But in fact，they really give me a lot of pressure．I still clearly remembered the happiness of my childhood．Unluckily，we had to face the fact with time passing by．We began to feel this invisible(无形的)pressure come upon us．We get up before sunrise and return after sunset．we work and study like an adult，even harder．What we do is to get an excellent mark．Oh，growing up is completely boring．We must try to find happiness while growing up．I think the friendship among our friends，the support from our parents and the encouragement from our teachers can help us．Why not enjoy the pleasure of growing up and its delicious taste