**Core Concept**
The demographic goal of Net Reproduction Rate (NRR) equal to 1 implies that, on average, a woman is replacing herself with one daughter, ensuring a stable population size. Achieving this goal requires effective family planning and contraceptive measures.

**Why the Correct Answer is Right**
To achieve NRR=1, the couple protection rate (CPR) must be sufficiently high to prevent unintended pregnancies. CPR measures the percentage of women of reproductive age using modern contraceptive methods. If CPR is low, many couples will not use protection, leading to unintended pregnancies and higher birth rates. A CPR of at least 60% is often cited as a threshold for achieving NRR=1, as it ensures that the majority of reproductive-aged women are using effective family planning methods.

**Why Each Wrong Option is Incorrect**
**Option A:** 30% - This CPR is too low to achieve NRR=1, as many couples will not use protection, leading to unintended pregnancies and higher birth rates.
**Option B:** 50% - While this is an improvement over 30%, it is still not sufficient to achieve NRR=1, as a significant proportion of reproductive-aged women will not be using effective family planning methods.
**Option C:** 80% - This is higher than the recommended threshold and would likely lead to a decline in population growth rates, but it is still a feasible target for many countries.

**Clinical Pearl / High-Yield Fact**
A CPR of at least 60% is often cited as a threshold for achieving NRR=1, but the exact target may vary depending on the country's population growth goals and other demographic factors.

**Correct Answer: C. 80%**