Explanation:

Correct answer is (d). Connector I If one word could describe a person, for the former Prime Minister Atal Vihari Bajpayee it would have been the way he used to compromise.
It is correct as it makes meaningful sentence. Connector II: As one word can describe a person, for the former Prime Minister Atal Vihari Bajpayee it would have been the way he used to compromise.
This is incorrect as the beginning phrase makes assumes that one word can actually describe a person. This is subjective and not a fact and thus the statement does not make sense. Connector III: Hardly one word can describe a person then for the former Prime Minister Atal Vihari Bajpayee it would have been the way he used to compromise. It is completely irrelevant as the statement developed is not meaningful.
This makes option D the right choice among the given options.