Step 1: PCR Fundamentals. Polymerase Chain Reaction (PCR) is a molecular biology technique for amplifying specific DNA segments, involving a series of temperature-dependent stages. Step 2: Core PCR Stages. - Extension (A): DNA polymerase synthesizes a new DNA strand complementary to the template strand at an optimal temperature for enzyme function. - Annealing (B): Primers (short DNA sequences) bind to their complementary sequences on the single-stranded DNA template at a lower temperature. - Propagation (C): This term typically denotes replication; in PCR, it can refer to DNA segment amplification by polymerase during the extension phase. - Denaturation (D): High temperature is applied to the DNA template to break hydrogen bonds between complementary strands, rendering them single-stranded. Step 3: Summary. Extension, Annealing, Propagation, and Denaturation are all essential components of the PCR process. Final Answer: \[\boxed{\text{The correct answer is (3) (A), (B), (C) and (D).}}\]
