A plane is a two-dimensional construct. Extending a three-dimensional figure in all directions infinitely will not result in two dimensions; therefor the answer is not plane.
A line is a one-dimensional construct. This means it is not the correct answer.
A point has no dimension. This means it is not the correct answer.
Extending a three-dimensional figure in all directions infinitely will encompass all 3 dimensions, meaning the correct answer is space.
