单选题 All flights ______ because of the snowstorm, many passengers could do nothing but take the train.
  • A. had been canceled
  • B. have been canceled
  • C. were canceled
  • D. having been canceled
【正确答案】 D
【答案解析】[解析] 该题为“逻辑主语+doing”构成主语独立结构，表示原因。