In PCR, which combination of statements is true?

• A. I, II, III
• B. I, II, IV
• C. II, III
• D. II, IV

Answer: (D)

PCR amplifies a specific DNA fragment by cycling through denaturation, primer annealing, and extension with a thermostable DNA polymerase. Each cycle uses a template, primers that flank the target region, dNTPs, and a suitable buffer, and the amount of product grows roughly exponentially because each new double-stranded molecule can serve as a template in subsequent cycles. The correct combination will include statements that reflect these essentials—the need for a template, primers, enzyme that works at high temperatures, and the cycle steps—and will exclude statements that conflict with these fundamentals (such as requiring RNA instead of DNA, or claiming amplification happens in a single cycle).

I don’t have the exact wording of the statements II and IV. Please share their text, and I’ll explain why that pair is the best choice and how the others would not fit.