How did Indus River Valley civilizations use irrigation techniques? Please answer I need this for a big test

An education expert is researching teaching methods and wishes to interview teachers from a particular school district. she randomly selects ten schools from the district and interviews all of the teachers at the selected schools. which type of sample did she use in this study? a)systematic sample b)probability sample c)stratified sample d)cluster sample

Journey stations were established throughout the mongol empire every miles.

According to justice brown's opinion, social equality must be the result of what three factors?