Hint: Polymerase chain reaction is the laboratory technique in which a double stranded DNA molecule is separated into two single stranded molecules and the enzyme which is used in this technique is called Taq polymerase.
complete solution: Option A Amplification of DNA: Polymerase chain reaction also known as PCR is the laboratory technique widely used worldwide as this technique can produce millions to billions copies of specific DNA samples. There are different methods of PCR, but the majority of methods rely on thermal cycling. Option B Amplification of enzyme: The technique used for enzyme amplification is known as Nicking enzyme amplification reaction (NEAR) and is used for DNA amplification. Do you know that enzyme amplification is important as it is used in diagnosis of diseases and monitoring of clinical conditions? Option C Amplification of Protein: Protein cannot be amplified with the help of Polymerase chain reaction. PCR is the technique which can be used for amplification of DNA. Option D All of these: As we know that Polymerase chain reaction also known as PCR is the laboratory technique widely used worldwide as this technique can produce millions to billions copies of specific DNA samples. So, from this it is not used for amplification of both enzymes and proteins.
Hence option A is the correct answer.
Note: Amplification is the technique used in molecular biology and it is the process in which molecules of nucleic acids are copied enzymatically to generate a progeny which is like the parent one. Polymerase chain reaction is the most widely used amplification technique.