Answer:
Line = To get a Unique line you need two distinct points.
In the given figure PQ is a line.
A plane is either a two dimensional or three dimensional surface such that if you take any two points on it ,the line joining these two points will completely lie on it.
You can name a plane by Single Alphabet or Set of Alphabet.
So,the plane can be Named as: P,Q,R , S→Single Alphabet or
P Q,PS,SR, R Q,→Using two Alphabet,
→ P QR, P Q S,......,P Q RS.
