Select the correct answer. In which research method does a researcher change the value of one variable to determine how the change affects another variable?

Which set of lines provides the best textual evidence for why death ought not be proud? a)and soonest our best men with thee do go, rest of their bones and souls' delivery! b)one short sleep past we wake eternally and death shall be no more: death thou shalt die! c)death be not proud though some have call'd thee mighty and dreadful for thou art not so: d)from rest and sleep which but thy picture be 5 much pleasure then from thee much more must flow