When a historical record is not dated, which two methods might historians use to check its authenticity

Which describes a domestic policy for which president nixon was responsible? the reduction of tension between the democrats and republicans the establishment of the second frontier the reduction of tension between the united states and china the establishment of the environmental protection agency

Describe the technology advancements that lead to explorers being able to sail great distances. [[ps: doesn't explain where. i am only speculating it's in europe.

With state which alliance promoted goals and protection of the united states and which alliance promoted goals and protection of the soviet union. site and explain evidence from each primary source to support your answers.