這三個(gè)短語都是被動(dòng)結(jié)構(gòu)：
1.be connected to :把...連上,例如,Please connect the computer to the Internet.
2.be connected with :把...與...連接起來.例如,It serves as a bridge which connects the mainland with the rest of the world.(它是連接祖國(guó)大陸與世界其它地方的橋梁）.The mainland is connected with the rest of the world.
3.be connected by：被...連接在一起.例如,The whole world is connected with by computers and it is becoming smaller and smaller.(整個(gè)世界被電腦連在了一起,世界變得越來越小了）.
祝你一切順利!