**Core Concept**
The Net Reproduction Rate (NRR) is a demographic measure that indicates the number of daughters a woman would have in her lifetime, assuming a fixed population and constant fertility and mortality rates. Couple Protection Rate (CPR) is the percentage of couples using some form of modern or traditional contraceptive method.

**Why the Correct Answer is Right**
For the NRR to be 1, the population should be replacing itself, meaning that each couple, on average, should be having two children (considering both sexes) to replace themselves. Since not all couples use contraception effectively or consistently, a higher CPR is needed to achieve a lower total fertility rate (TFR).

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a lower CPR would not be sufficient to reduce the total fertility rate to replacement level.
**Option B:** Similarly, this option is also incorrect as it does not provide adequate coverage to reduce fertility rates to the desired level.
**Option D:** This option is incorrect because it exceeds the required threshold, implying more than enough contraceptive coverage for replacement fertility.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that achieving an NRR of 1 requires careful consideration of fertility rates, mortality rates, and the effectiveness of contraceptive methods.

**Correct Answer:** Correct Answer: C. 60%