Because cells are in ever living thing
Answer:
Nothing
Explanation:
A. Control variables generally entail little or no system change. To see if the method worked, the researchers required a positive control in which the heat-killed virulent bacteria invariably transformed the non-virulent microorganisms. This positive control involves adding "nothing" to both the heat-killed virulent bacteria before mixing them with the non-virulent bacteria.
A heart attack happens when a coronary artery becomes out of no where in a instant blocked and it stops the flow of blood to the heart muscle and starts to damage it.
