Experts believe that most native americans died of diseases like smallpox, typhoid, or diphtheria in the first decades of contact with european settlers. which statement best explains this phenomenon?

I would need to see the statments to be sure but i belive that the answer is,

eouropeans would travel to america on ships infested with rats carrieing these deadly diseases which is also to be belived that is why america has these diseases in the first place.