问题
选择题
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 be residents be permitted
D. the residents had been permitted
答案
答案：C
（2）环己烷（C6H12）有12种结构，其中含三元环（三角形）的有 种。