During negotiations, the Managing director remained obdurate.

The correct answer is A. adamant.

Adamant means refusing to change one’s opinion or course of action. In the context of the question, the managing director was unwilling to compromise during negotiations.

The other options are not as accurate. Tough means firm or severe, but it does not necessarily mean unwilling to compromise. Cooperative means willing to work with others, but it does not necessarily mean being easy to negotiate with. Flexible means able to change easily, but it does not necessarily mean being willing to give in to demands.