Answer:
B). I started to do voluntary work three years ago.
Step-by-step explanation:
The second option correctly transforms the given sentence into the past using past indefinite tense. Past indefinite tense is employed to denote the actions that occurred or happened at a particular point of time in the past('started to do voluntary work three years ago'). It is framed using 'subject + V2 + object.' While present perfect tense is employed to denote an action that began in past but still progressed till now. Such actions carry their effects in the present which cannot be possible in the given context as the action took place entirely in the past. Thus, option B is the correct answer.