When Did Einstein Originally Introduce His Theory of General Relativity

When did Einstein originally introduce his theory of general relativity, including the cosmological constant?

A) in 1896, before the modern stellar spectral classification scheme was devised
B) in 1915, before the question of the nature of the Milky Way Galaxy had been resolved
C) in 1930, after Hubble had discovered evidence for the expanding universe
D) in 1968, after the discovery of the cosmic microwave background gave evidence of the Big Bang