How can the constant function $y = 9$ be written in the standard linear form $y = mx + b$?

It cannot be written in this form.

Which statement accurately describes the function $y = -4$?

It is a linear function with a slope of -4.

It is a linear function with a slope of 0.

It is not a linear function because there is no $x$ term.

It is a linear function with an undefined slope.

Yes, because its graph is a horizontal line with a slope of 0.

No, because a linear function must include the variable $x$.

No, because its graph is a single point.