Answer:
Postulate 2
Explanation:
Postulates related to the line determined by two points are postulates 1, 2 and 4.
Postulate 1 supposes that line is already given, but in your question line is not given - it must be determined.
Postulate 2 is the correct option, because it says that through any two different points, exactly one line passes.
Postulate 4 determines the position of the line passing through these points, not its existence.