Select the postulate that states points a and b lie in only one line.
postulate 1: a line contains at least two points.
postulate 1a: a plane contains at least three points not all on one line.
postulate 1b: space contains at least four points not all on one plane.
postulate 2: through any two different points, exactly one line exists.
postulate 3: through any three points that are not one line, exactly one plane exists.
postulate 4: if two points lie in a plane, the line containing them lies in that plane.
postulate 5: if two planes intersect, then their intersection is a line.