题目

Not until the train pulled into the next station ______ her suitcase gone. A. Mary had found                B. had Mary found C. did Mary find                     D. Mary found   答案：C 我国居民建筑北方多平顶房，南方多人字顶房，造成这种差异的主要原因是（   ）      A.地形        B.气温        C.降水        D.人口