Question:
A point $C$ is called the mid-point of a line segment $\overline{A B}$ if
(a) C is an interior point of AB
(b) AC = CB
(c) $C$ is an interior point of $A B$, such that $\overline{A C}=\overline{C B}$
(d) AC + CB = AB
Solution:
(c) C is an interior point of AB, such that AC = CB