Please help me i don't know the answer to this

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

Ireally need on this homework! if you get it right so much if not its fine < 3 ! (i have no points so sorry its only 10)i didnt mean to put it on social studies sorry!

What does it mean to say that "service sector" jobs are predominant in europe's mixed economies today? a. that jobs where people work in factories predominate b. that jobs where people do something for others predominate c. that jobs where people work the land predominate d. that jobs in government predominate