I don’t think this is case of subjunctive. A subjunctive requires a mandate, or wish or some such thing but certainly 'a belief' is not one among them. Secondly a present subjunctive has to necessarily have a subordinate clause introduced by the connector that. Thirdly and compulsorily, the verb of the subordinate clause will have to be in the imperative mood, meaning, in the base form of the verb. An infinitive form such as
'to be capable' of is not a subjunctive verb.
I feel the debate here is between whether '
to be capable of' is right or '
are capable of' is right. I wouldn’t think there is any significant difference between them; I would rather go with B because of the certainty of the stem cells' capability that the choice exudes. C is out for using the future tense;
More importantly, D and E have a fatal grammar error. As written, both the participles that modify stem cells “
derived from, and believed as/ to be capable of’ are required to be necessarily joined by a conjunction ‘
and”; otherwise, the second participle will be simply dangling as a run–on. So D and E can be dumped.