Answer:
C. sentence 3
Step-by-step explanation:
English sentences have either active or passive voice. When the subject of a sentence does an action, the sentence is active. For example: Mike wrote a letter to his friend.
The sentence has passive voice when the subject receives an action. Like: A letter was written by Mike.
Formula of passive voice: (to be)+ past participle
Sentence 3 (a priceless painting is stolen by the thieves) has a passive voice; verb 'is' and 'stolen, past participle of steal'.