Short Answer: A Remark C Let's start with the false choices. If they were colinear, then if AB + BC would = 5 or 1 depending on the location of C. Answer C is not correct.
B a b and c do not form a right triangle. a^2 + b^2 ≠ c^2 2^2 + 3^2 = 13 not 16 (which is what c^2 or 4^2 = )
D D is false. Equilateral triangles have 3 equal sides.
A is true. Since A and C are opposites and you have eliminated C by arguing A. Then A must be the answer.