Why is the sa node called the pacemaker of the heart?

Consider the last statement in the prompt: "people take such environmental factors into account in their choices when deciding where to live." do all people have a choice as to where they live? what factor plays a key role in this decision and may therefore play a large role in determining quality of life?

The intervention of extraterrestrials has been used to explain the bermuda triangle, a region of the atlantic ocean where ships and planes are frequently lost, leaving no evidence behind. how would this explanation best be characterized?

2. given that most biochemical (other than coal) rocks react with hydrochloric acid, what does that tell you about organisms?