参考答案

正确答案：D
解析：本题询问犯人是以怎样的方式来表明他们的工作态度的。相关语句为第二段的“far more volunteers were forthcoming than could actually be employed”，“they would sometimes work through their lunch hour and tea break，and even carry on in the rain”，说明囚犯们工作态度是自觉自愿的。