hard的副詞形式是什么?

　　Hard work never hurt anyone.

　　努力工作絕無害處。

　　That's a very hard question.

　　那是個很難的問題。

　　It's pretty hard to explain.

　　這事很難解釋清楚。

　　I find that hard to believe.

　　我對此感到難以相信。

　　His father was a hard man.

　　他父親是個冷酷無情的人。