It surprised us ___ there was so little stone in the wall —-all the construction material was of mud brick（） A: wihich B: who C: whom D: that

It surprised us ___ there was so little stone in the wall ----all the construction material was of mud brick. A: wihich B: who C: whom D: that

‎It surprised us ___ there was so little stone in the wall ----all the construction material was of mud brick.‍ A: wihich B: who C: whom D: that