If a part of the line connecting two interior points that lie outside the polygon, then it is called ________.
A point C is called the midpoint of a line segment ¯¯¯¯¯¯¯¯AB if
(a) C is an interior of AB
(b) AC=CB
(c) C is an interior point of AB such that ¯¯¯¯¯¯¯¯AC=¯¯¯¯¯¯¯¯CB
(d) AC+CB=AB
Points that lie on a line are called :