--- full preparation,the doctor decided to postpone the oper

用现在分词的完成时态,表示分词的动作prepare发生在主句动作(decided)之前,相等于说：
Because the doctor had not prepared, he decided to postpone the operation.
如果直接用现在分词,分词的动作和主句的动作是同时发生的,例如：
Taking the umbrella, she rushed out of the door.
再问： 那为什么不用made 呢
再答： 如果用过去分词，则表示这个分词的逻辑主语（即主句的主语）和这个过去分词之间是被动的关系：Punished harshly by his mom, the girl cried hard.