hard的副词形式是什么?

　　Hard work never hurt anyone.

　　努力工作绝无害处。

　　That's a very hard question.

　　那是个很难的`问题。

　　It's pretty hard to explain.

　　这事很难解释清楚。

　　I find that hard to believe.

　　我对此感到难以相信。

　　His father was a hard man.

　　他父亲是个冷酷无情的人。