Blood donations can be used to save lives for people suffering from blood loss due to traumatic injury. However, other times only certain components of the blood are needed. For example, platelets can be donated and used to help in cases where a clotting factor is missing in a patient. The fractioning of blood into its components is shown here. What experimental design was most likely used to provide evidence for the success in blood fractioning?

A) Blood donations were collected and separated by their different sizes.
B) Blood donations were collected and separated by the temperature at which they boil.
C) Blood donations were collected and separated by their attraction to a magnetic field.
D) Blood donations were collected and separated by their different densities in the mixture.