What makes this source credible? Explain with evidence from the sourcing information Captionless Image

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

Doing the text now can someone me

This refers to weather and atmospheric conditions measured over a long period of time.