sad的副词形式是什么

　　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。

　　It was sad to see them go.

　　看着他们离去，真让人难过。

　　You'd have to be sad to wear a shirt like that.

　　你穿着那样的衬衣显得老气。

　　I was very sad indeed to hear of your father's death.

　　听到令尊大人去世，我感到非常难过。