Final answer:
A constant variation between two quantities denotes a linear relationship, which is described by the slope and y-intercept in the linear equation form y = mx + b or y = a + bx.
Step-by-step explanation:
When there is a constant variation between two quantities, it indicates a linear relationship. In the context of linear equations and graphing, this relationship is represented by the equation y = mx + b or y = a + bx.
In these equations, the coefficient m (or b in the statistical form) represents the slope of the line, which describes how much the dependent variable (y) changes for every unit increase in the independent variable (x). The constant b (or a in the statistical form) is the y-intercept, which indicates the value of y when x is zero, or where the line crosses the y-axis.
Therefore, when there is constant variation between two quantities, the correct answer to this question is a) A linear relationship.