The correct answer is: A. 1929
Dhanbad district was created in 1929 by the Government of Bihar. It was carved out of the districts of Manbhum and Hazaribagh. The district is named after its headquarters, Dhanbad, which is a major coal mining town.
Option B is incorrect because Dhanbad district was not created in 1986. In 1986, the Government of Bihar created the new district of Bokaro by carving out some parts of Dhanbad district.
Option C is incorrect because Dhanbad district was not created in 1991. In 1991, the Government of India created the new state of Jharkhand by carving out some parts of Bihar, including Dhanbad district.
Option D is incorrect because Dhanbad district was not created in 1956. In 1956, the Government of India reorganized the states of India, but Dhanbad district remained in the state of Bihar.