I concur with above reply as regards D's appointment as director of the Company.
However, firstly check up your Shareholders Agreement, it may provide for some mechanism in case of such eventualities.
Absent any mechanism in the agreement- Normally it is and I believe that it would be so in your facts as well that there will be multiple other acts on part of other directors and shareholders that C/D must be finding prejudicial to their interests; there likely will be other issues as well.
If D can make out a case that the affairs of the company are being conducted in a manner prejudicial to his interest and in an oppressive manner, he can, being a member holding more than 10% equity in the Company, file an application u/s.241/242 of Companies Act, 2013 before NCLT concerned. U/s.242, NCLT has powers to appoint/ remove directors in a proper case and could grant host of other reliefs.
In a 50:50 voting resulting in a deadlock will also create issues in appointment of new directors at AGM and in that situation also, NCLT could be approached for different reliefs.
I suggest that you may approach a lawyer with all attendant papers and facts for final advice and pursuing a suitable remedy.