## **Core Concept**
The question pertains to the properties of a normal distribution, specifically in the context of systolic blood pressure (BP) among a population. In a normal distribution, about 68% of the data falls within one standard deviation of the mean, about 95% falls within two standard deviations, and about 99.7% falls within three standard deviations.

## **Why the Correct Answer is Right**
Given that the mean systolic BP is 120 mm Hg and the standard deviation is 10 mm Hg, we can apply the 68-95-99.7 rule. This rule implies that:
- About 68% of the population will have a systolic BP between 110 mm Hg (120 - 10) and 130 mm Hg (120 + 10).
- About 95% of the population will have a systolic BP between 100 mm Hg (120 - 2*10) and 140 mm Hg (120 + 2*10).
- About 99.7% of the population will have a systolic BP between 90 mm Hg (120 - 3*10) and 150 mm Hg (120 + 3*10).

## **Why Each Wrong Option is Incorrect**
- **Option A:** Without specific details on the range provided in option A, it's hard to directly refute it based on the information given. However, if it suggests a percentage or range not consistent with the 68-95-99.7 rule, it would be incorrect.
- **Option B:** Similarly, without specifics, if option B does not align with expected ranges or percentages based on the standard deviation and mean, it's incorrect.
- **Option C:** This option would be incorrect if it does not accurately reflect the application of the 68-95-99.7 rule or other statistical properties of the normal distribution.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is the 68-95-99.7 rule for normal distributions, which helps in quickly estimating the spread of data. For instance, in the context of blood pressure, understanding that about 95% of the population falls within two standard deviations of the mean can help in identifying individuals with significantly elevated or decreased blood pressure.

## **Correct Answer:** D.