question: Q:An investigator is processing a blood sample from a human subject. A reagent is added to the sample and the solution is heated to break the hydrogen bonds between complementary base pairs. This solution is then cooled to allow artificial DNA primers in the solution to attach to the separated strands of the sample DNA molecules. An enzyme derived from the thermophilic bacterium Thermus aquaticus is added and the solution is reheated. These steps are repeated multiple times until the aim of the test is achieved. The investigator most likely used which of the following laboratory procedures on the test sample?? 
  {'A': 'Polymerase chain reaction', 'B': 'Immunohistochemistry', 'C': 'Northern blot', 'D': 'Western blot', 'E': 'Fluorescence in-situ hybridization'},