Why Were Both the Elections of 1976 and 1983 Hailed

Why were both the elections of 1976 and 1983 hailed as a new era of 'parity politics'?

A) Because opposition parties formed governments on both occasions
B) Because the Japan Socialist Party gained huge numbers of seats in parliament
C) Because the LDP failed to secure outright majorities in both elections
D) Because voters began to choose their representatives based on their environmental credentials.