Answer:
Option c.
Explanation:
The set of points (x, y, z) such that z = 6.
So, all pairs are in the form of (x,y,6).
where, x and y can be any real number.
It the set of points (x,y,6), z-coordinate is constant.
So, it represents a plane parallel to xy-plane and the distance of this plane from the xy-plane is 6 units.
Therefore, the correct option is c.