How do i solve this problem? can someone ?

Which were difficulties that the builders of the transcontinental railroad found ways to overcome? Select all the choices that apply.

Out of all the options presented above the ones that represent the difficulties that the builders of the transcontinental railroad found ways to overcome are answer choices A) providing supplies to build the tracks and support the workers and B) natural barriers such as mountains, rivers, and forests. It was also the same reason why the transcontinental railroad was being constructed. It would help the transportation of  if this is hitory i dont know what subject this is but if its history heres the answers