**Frequency Polygon**

A frequency polygon is a type of graph that represents the distribution of a dataset. It is constructed by connecting the midpoints of the tops of the bars in a histogram with line segments. The horizontal axis represents the values of the variable being measured, and the vertical axis represents the frequency or count of each value.

**Coordinate Axes**

The coordinate axes in a graph are the two lines that intersect at the origin and provide a reference for plotting data points. The horizontal line is called the x-axis, and the vertical line is called the y-axis.

**Understanding the Options**

a) either of the coordinate axes
b) the x-axis
c) neither of the coordinate axes
d) the y-axis

**Option A: Either of the coordinate axes**

This option suggests that one of the sides of a frequency polygon can be either the x-axis or the y-axis. However, this is incorrect because the x-axis is the correct answer.

**Option B: The x-axis**

The x-axis represents the values of the variable being measured in a frequency polygon. It is the horizontal axis along which the midpoints of the tops of the bars in the histogram are connected to form the frequency polygon. Each midpoint represents a value of the variable, and connecting them with line segments creates the polygon. Therefore, option B is the correct answer.

**Option C: Neither of the coordinate axes**

This option suggests that none of the sides of a frequency polygon can be the coordinate axes. However, as explained above, the x-axis is an integral part of constructing a frequency polygon.

**Option D: The y-axis**

The y-axis represents the frequency or count of each value in a frequency polygon. It is not a side of the polygon itself but is used to measure and represent the frequency values. Therefore, option D is not the correct answer.

In summary, the correct answer is option B - the x-axis. The x-axis is an essential component of constructing a frequency polygon as it represents the values of the variable being measured.