Answer:
D. We found that the houses had been looted, the bridges had been broken, and the farms had been burned.
Explanation:
Parallelism is arranging words of identical syntactical constructions.
'the houses had been looted'
'the bridges had been broken'
'the farms had been burned'
All three verbs are used in the Past Perfect Passive form, which means that their syntactical constructions are identical.