If two lines are coplanar, the following must be true:
- All points on the lines are coplanar.
However, it's important to clarify that while coplanar lines may intersect, they might also be parallel and never intersect, as long as they lie within the same plane.
So, among the statements provided, the one that must always be true about coplanar lines is:
- All points on the lines are coplanar.
The others are not necessarily true in all scenarios.