Which of the Following Is the Major Source of Preanalytical

Which of the following is the major source of preanalytical error when collecting capillary blood samples?

A) failure to collect enough sample for the analysis
B) failure to add anticoagulant to the capillary tube prior to collection
C) failure to mix the sample collected with anticoagulant in the capillary tube
D) failure to use only free-flowing blood from the puncture site