sad的比較級和最高級怎么寫

　　例句：

　　1、How sad that all his hard work should come to nothing.

　　他的所有辛勤勞動竟全部付諸東流，太讓人傷心了。

　　2、It's a sad fact that many of those killed were children.

　　讓人難以接受的是遇難者中很多是孩子。

　　3、It was sad to see them go.

　　看著他們離去，真讓人難過。