Answer:
↔
DC
↔
DB
↔
BC
Explanation:
To answer it, we must remember one axiom.
At least two points define a line.
Then I can call line p as (see below attached picture)
Since a line is infinite, and no thickness I can choose any two points that are elements of 'p' to represent it, just in case I don't want to represent it by a single letter of the Western Alphabet.