题目

. His first fight was for the equal rights of black people in South Africa．Then, as the first black president he fought to unite the country and organize the government. Now Nelson Mandela has set his sights on a new enemy, AIDS. On March 19 the 82-year-old, former president, hosted his second AIDS-awareness concert. He warned that 25 million people in Africa were already infected with the fatal disease. Mandela was born in a small village in South Africa in 1918．He was adopted by the chief of his tribe (部族) and could have been a chief himself and lived a happy country life. But he ref塑料挂钩是靠大气压将其压紧在光滑的墙上的．若挂钩表面积是5cm2，大气压是1atm，则大气压作用在挂钩上的压力是________N．