The correct answer is: 1956.
Tubewell irrigation work was started in Bihar in 1956. The first tubewell was installed in the state in the same year. The government of Bihar has been promoting tubewell irrigation as a means of increasing agricultural production. The state has also been providing subsidies to farmers for installing tubewells.
Option A: 1930 is incorrect because tubewell irrigation work was not started in Bihar in 1930.
Option B: 1950 is incorrect because tubewell irrigation work was not started in Bihar in 1950.
Option C: 1955 is incorrect because tubewell irrigation work was not started in Bihar in 1955.
Option D: 1956 is correct because tubewell irrigation work was started in Bihar in 1956.