Why Bilbo?

I think gandalf picked bilbo because he knew that bilbo deep inside would really of liked and adventure. Of course I am not possitive about this, because I am doing a report on the Hobbit and need to know this yet I do not... So yes if anyone knows please respond! thank you very much!

I do agree with child... Maybe tolken didn't know why gandalf choose bilbo... If no one else knows then how do we know that he even knew himself?