Einstein Introduced a "Cosmological Constant" into His Formulation of the Structure

Einstein introduced a "cosmological constant" into his formulation of the structure of the universe as described by his general theory of relativity. How did he envision that the cosmological constant would manifest itself?

A) as many "white holes" that would contribute matter to an expanding universe to maintain constant density, as required by the cosmological principle-a continuous-creation universe
B) as an extra "gravity" that would hold the universe against continuous expansion
C) as antimatter that, by annihilating real matter, would translate matter into energy, thereby maintaining a constant mass density in a condensing universe
D) as a form of energy that, on its own, would make the universe expand-a form of antigravity