Every weekend is important to the Franklin's family. During the week they don't have very much time together, but they spend a lot of time together on the weekend.

    Mr. Frankin works at the shoe store downtown during the week, but he doesn't work there on the weekend. Mrs. Franklin works at the city hospital during the week, but she doesn't work there on the weekend.

    Bobby and Sally Franklin go to the junior high school during the week, but they don't go there on the weekend.

    And the Franklin's dog Rover stays at home alone during the week, but he doesn't stay at home alone on the weekend.

已知：点P是直线MN外一点，点A、B、C是直线MN上三点，分别连接PA、PB、PC．

（1）通过测量的方法，比较PA、PB、PC的大小，直接用“＞”连接；

（2）在直线MN上能否找到一点D，使PD的长度最短？如果有，请在图中作出线段PD，并说明它的理论依据；如果没有，请说明理由．