Which of the following BEST define linear relationship?

a.
Linear relationship increase in the values of one variable and accompanied by decreases in the values of the other variable.

b.
It is a statistical term used to describe a straight-line relationship between two variables.

c.
It describes a situation where there is not a straight-line or direct relationship between an independent variable and a dependent variable.

d.
It refers to how participants are allocated to the different groups in an experiment