The correct option is C Raining
Option A is the correct answer as the verb 'stop' requires an object and gerund 'raining' is acting as an object to the verb 'stop.' Also, the sentence is talking about an activity that continuously happened in the past. So, gerund, and not infinitive, can bring this sense from the sentence. This is why Option B cannot be used as it is an infinitive. Options C and D cannot be used as they will render the sentence grammatically incorrect.