The correct answer is C. Line graph.
A line graph is a type of graph that shows the relationship between two variables over time. The variables are typically represented by two axes, with the x-axis representing the time and the y-axis representing the value of the variable. The line graph is created by plotting the points that represent the values of the two variables at each time point.
A histogram is a type of graph that shows the frequency distribution of a variable. The variable is typically represented by the x-axis, and the frequency of each value is represented by the height of the bar at that value.
A frequency polygon is a type of graph that is similar to a histogram, but the bars are connected to form a line. This makes it easier to see the overall trend in the data.
A scatter graph is a type of graph that shows the relationship between two variables. The variables are typically represented by the x-axis and the y-axis, and each point on the graph represents a pair of values for the two variables.
Line graphs are the best way to show the trend for a variable because they can be used to show the relationship between the variable and time. This makes it possible to see how the variable has changed over time.