To the men and women who served in World War Ⅱ and the people they liberated, the G.I. was the common man grown into hero, the poor farm kid torn away from his home, the guy who bore all the burdens of battle, who slept in cold foxholes, who went without the necessities of food and shelter, who stuck it out and drove back the Nazi reign of murder.请问划线部分是什么句子成分（ ）。