What Method Is Being Used to Discover Whether This Is

Multiple Choice

What method is being used to discover whether this is an unbounded universe, in which expansion will continue forever, or a bounded universe, in which expansion will eventually turn into contraction and lead to recollapse?

A) careful monitoring of the Moon-Earth distance to detect the slowdown of the expansion of the universe
B) measurement of the deviation from uniformity of the cosmic background radiation
C) measurement of the brightnesses of distant supernovae
D) measurement of the bending of light by distant galaxies as it follows the curvature of space