Answer:
d. rectangular
Step-by-step explanation:
Because it is the simple one and is used the most in calculations.
For example, if we want to make an equation of straight line, it would be like
![y=m*x+c](https://img.qammunity.org/2021/formulas/engineering/middle-school/4m95fdqyddpo0vp0rqi2hqw494tcetnagb.png)
here
y=vertical axis
x=horizontal axis
m= slope of straight line
c=point on y axis where line is cutting y axis
Hence, rectangular coordinate system is the simplest one and is used most commonly.