In Geometry, when two planes intersect, their intersection is a line; and any two distinct points determine a line. These are fundamental concepts describing the relationships between geometric figures.
The subject of the student's question is Geometry, which is a branch of Mathematics. Specifically, the question pertains to geometric postulates that describe relationships between figures.
The first postulate to complete is: If two planes intersect, then their intersection is a line. This is because any intersection of two planes in three-dimensional space is a line, assuming that the planes are not parallel and indeed do intersect.
The second postulate to complete is: Any two distinct points determine a line. This tells us that through any two points, there is exactly one line that passes through both of them. This is a fundamental concept in geometry.