The Flatness Problem Is That

The flatness problem is that

A) the density of the universe is very close to the critical density.
B) the density of the universe is much larger than the critical density.
C) the flat universe would expand forever,and we could never measure the density of the universe.
D) the laws of physics may not be different at different times in the history of the universe.
E) the red shift of a distant galaxy is caused by the curvature of space-time.