The word 'while' refers to two actions that happened simultaneously. Hence both will be in past tense.
Option A: 'Was stolen' is in simple past tense in passive voice. It states an action 'stolen' experienced by the subject 'my camera'. It is relevant to the given sentence which refers to past time. Hence option A is correct.
Option B: 'Has been stolen' is in present perfect tense. It states an action that just happened. But the sentence is in past tense.
Option C: 'Is stolen' is in simple present tense, whereas the action is in the past.
Option D: 'Stole' is a simple past tense verb in active voice. A sentence is active when the subject 'camera' performs the action. Here it receives the action 'to be stolen', since the subject 'camera' cannot perform the action 'to steal'.
Hence options B, C and D are wrong.