The answer is A .
PCR stands for Polymerase Chain Reaction. It is a method to analyze a short sequence of DNA or RNA and is used to reproduce (amplify) selected sections of the nucleic acid. Untold numbers of copies can be made of the DNA in just a few hours.
PCR amplifies the regions of DNA that it targets and can therefore be used to analyze extremely small amounts of sample. This is often critical for forensic analysis, when only a trace amount of DNA is available as evidence.
