A researcher was trying to amplify a DNA fragment in vitro using a polymerase chain reaction (PCR). All the required components for the reaction except the Taq DNA polymerase were available. The experimenter decided to use DNA polymerase isolated from E. coli instead of Taq DNA polymerase. The E. coli polymerase was added to the reaction at the extension step of each cycle of the PCR. In this scenario, from the options given below, the optimal temperature to be set in the extension step of the PCR is:

• A

  $72{ }^{\circ} \mathrm{C}$
• Correct answer
  B

  $37{ }^0 \mathrm{C}$
• C

  $25{ }^0 \mathrm{C}$
• D

  $92{ }^{\circ} \mathrm{C}$

Hence, the correct answer is option: 'B'.