If Space Were Flat and There Were No "Dark Energy

Multiple Choice

If space were flat and there were no "dark energy," what would be the future of the universe?

A) The universe would expand forever, but only barely; if it had any more matter in it than it does, it would eventually stop expanding and start to collapse.
B) The universe would expand to a maximum size and then collapse into a Big Crunch.
C) The future of the universe is not related to the geometry of space.
D) The universe would have more than enough energy to expand forever, not stopping even when infinite time has elapsed.