Why has the social security act lasted so long?

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

The vietnam war was considered by many to be america’s first unopposed win independent war defeat

Canada economy usa test prep i am stupid i don’t get it