## **Core Concept**
The question tests the understanding of statistical methods used to demonstrate relationships between two continuous variables, specifically height and weight in children. The goal is to identify the most appropriate method for showing an association between these variables.

## **Why the Correct Answer is Right**
The correct answer, **C. Scatter diagram**, is right because a scatter diagram (or scatter plot) is a graphical representation that uses dots to represent the values obtained for two different variables – one on the x-axis and the other on the y-axis. This method is particularly useful for showing the relationship or correlation between two continuous variables, such as height and weight. Each point on the scatter plot represents a single observation in the dataset, allowing for a visual assessment of the relationship between the variables.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not specify a known statistical method or graph type used for demonstrating associations between variables.
- **Option B:** This option is incorrect as it also does not specify a standard method used for this purpose.
- **Option D:** This option is incorrect because, although it might seem plausible, it does not accurately represent the best method (scatter diagram) for demonstrating the association between two continuous variables like height and weight.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that correlation does not imply causation. When using a scatter diagram to show an association between height and weight, it's essential to consider other factors that might influence this relationship and to use statistical tests (like Pearson's r) to quantify the strength and direction of the correlation.

## **Correct Answer:** . Scatter diagram