What did Bret Harte mean when he wrote “half a world behind each back”?

Which type of evidence would support the author's claim?

Dr. robbins wants to know if there are different opinions regarding the value of public school education between native americans who have at least one relative who attended indian boarding school and native americans who have no family experience with indian boarding school. dr. robbins contacts 35 native american participants in each group. he wants each group to include younger as well as older adults, and a mix of male and female participants. he asks each person to complete a survey about their attitudes toward public education. the design of this study is:

Allow of the following ideas were regarded in the creation of the u. s. founding documents except