## Core Concept
The core concept being tested here is the understanding of confidence limits in relation to standard deviation (SD) in statistics, particularly in the context of medical research and data analysis. Confidence limits are crucial in estimating the range within which a population parameter is likely to lie.

## Why the Correct Answer is Right
The correct answer, , corresponds to the 95% confidence interval when the standard deviation is known. In a normal distribution, about 95% of the values lie within 1.96 standard deviations of the mean. This is a fundamental concept in statistics and is widely used in medical research to estimate the precision of an estimate. Given that the standard deviation (SD) is 2, the 95% confidence limit would indeed be calculated as mean ± (1.96 * SD), but for simplicity and general understanding, it's often approximated as mean ± 2SD for a quick estimation.

## Why Each Wrong Option is Incorrect
- **Option A:** This option does not correctly represent a commonly used confidence limit in medical statistics.
- **Option B:** This option might seem plausible but does not accurately reflect the standard confidence limit used in most medical research contexts.
- **Option D:** This option suggests a wider range than typically used for a 95% confidence interval and does not align with standard practices for estimating confidence limits.

## Clinical Pearl / High-Yield Fact
A key point to remember is that for a 95% confidence interval, if you approximate, you can use the rule of thumb that about 95% of values lie within 2 standard deviations of the mean. This can be a quick mental math tool in clinical and research settings.

## Correct Answer Line
**Correct Answer: B.**