How do researchers select a sample that is representative of its population

Northern was a learned a fairly cold climate caused by see one from the atlantic ocean, but se was real and tends to be much warmer, sonia look good causes difference. a.cool wins cannot blow across a leg into the south mountains, b.prevent cold air from blowing over into south sea,c.the south is at much higher elevation, so it is closer to the sun, d.suppose early and has a sperience a drastic climate change in the past few years.