The correct option is D having
Out of the four options, D is the correct option. The given sentence is the case of continuous infinitive which is used to express a continuing action after a verb or auxiliary which must be followed by the infinitive. Continuous infinitive is formed : verb + to be + infinitive. Here, 'seem' is the verb which is followed by to be and infinitive. Thus, options A, B and C are incorrect according to the rule.