sad的比较级和最高级怎么写

　　例句：

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

　　他的所有辛勤劳动竟全部付诸东流，太让人伤心了。

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

　　让人难以接受的是遇难者中很多是孩子。

　　3、It was sad to see them go.

　　看着他们离去，真让人难过。