I believe it to be 3.
2 is an english mastiff.
4 looks like boxers
1 is a possibility, but his neck looks too long in the photo and his shoulders too tall. Maybe a corso... but i could be horribly off.
1 is a Dogo Argentino
It's a trick question. American pitbull terriers are smaller dogs than all of these and have a different muzzle shape.
Its very hard to tell the size of 3 without anything for reference, but he looks pretty short to me.
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