问题补充：
It was announced that only when the fire was under control to return to their homes.
A. the residents would be permitted
B. had the residents been permitted
C. would the residents be permitted
D. the residents had been permitted
答案：
A. the residents would be permitted
B. had the residents been permitted
(答案→)C. would the residents be permitted
D. the residents had been permitted
解析：考查倒装句。Only+状语/状语从句位于句首，主谓应部分倒装。可排除A、D，居民被允许回到家园不可能发生在火势被控制之前，故不能用过却完成时。
