单选题 Mary ______ that the purchase had been a mistake. However, she didn't.
  • [A] ought to acknowledged
  • [B] ought to have acknowledged
  • [C] should acknowledge
  • [D] should be acknowledging


【正确答案】 B
【答案解析】情态动词题。ought to have acknowledged表示本应该做的事情，而没有做，与本句句意相符。