As per the paragraph given, which party was the main opposition party inside the Bihar legislature?

The post-independence land-reforms were adopted broadly on the basis of the Kumarappa Committee. This Committee took, as its guiding principle, the elimination of exploitation and giving the land to the tiller. Bihar Pradesh Kisan Sabha (BPKS) was founded in 1929. It established a national presence in 1936 as the All India Kisan Sabha (AIKS). Swami Sahajanand Saraswati dominated the provincial organisations, and emerged as the foremost Kisan leader in India, and also headed BPKS in 1935. The formation of the Congress Ministry in Bihar in 1937 accelerated the process of showdown between the two organizations. Zamindars offered their help and co-operation in passing tenancy laws to improve the condition of the tenants. The post-colonial India including Bihar witnessed the emergence of the Congress as the dominant party in the political system. In 1952 elections, Jharkhand Party was the main opposition party inside the state legislature. The important consequences of the 1952 general elections in Bihar were the emergence of two regional political parties, the Jharkhand Party and the Janta Party. The Janta Party was founded in 1950 by Raja Kamakhya Narayan Singh to build up a traditional opposition to Congress. Its political influence was confined mainly in south-Bihar. Until 1967, Bihar witnessed a one party dominance system i.e. the 'Congress system' as conceptualized by Rajni Kothari. Between 1967-69, elections witnessed a highly fractionalized multi-party system. The decline in the Congress electoral strength benefitted socialists and communists on the one hand, and the Jan Sangha on the other hand.