(1) First prove △ACO≌BDO, and get CO=DO, AO=BO, so CO+BO=DO+AO is the conclusion.

(2) all four.

(3) Because they are complementary angles of angle BAC, angle ABF= angle ACG. According to SAS certificate △ ABF △ ACG,

So angle BAF= angle G, angle GAE+ angle G=90, so the conclusion holds.