The variable that is deliberately changed, also known as the manipulated variable.

answer; i believe that the best answer is (secondary cardiac arrest due to

it is either c or d and i know for sure it is not a or b

the menstrual cycle – higher tier. negative feedback mechanisms affect the production of hormones in the menstrual cycle. oestrogen also stimulates the release of lh (luteinising hormone) from the pituitary gland, which in turn controls the production of progesterone.