Aplane is an undefined term because it
a: can be named using three noncollinear points

b: is described generally, not using a formal definition

c: is where other geometric shapes can be constructed

d: is a flat surface that extends indefinitely in all directions

Neither A, B or D explains why plane is undefined. All 3 of those answers describe something about plane which is true. Plane indeed can be named using three non collinear points. However, B is telling why plane is undenified. I it described generally, not using a formal definition.

Answer is B