Question

Define perpendicular lines.
A.
Lines that cut across two or more lines

B.
Two coplanar lines that do not intersect

C.
Two coplanar lines that intersect at a 90-degree angle

D.
Two non-coplanar lines that do not intersect

Answer 1

C. Two coplanar lines that intersect at a 90-degree angle.

(Briefly: A describes a transversal, B describes parallel lines, and D describes skew lines.)