How Does the Addition of a Nonzero Cosmological Constant Affect

Multiple Choice

How does the addition of a nonzero cosmological constant affect the expansion of the universe?

A) It is possible for the mass density of the universe to be below the critical density and still collapse.
B) It is possible for the density of the universe to be below the critical density and still expand forever.
C) It is impossible to have a collapsing universe,regardless of its density.
D) It is impossible to have an expanding universe,regardless of its density.