单选题 If the letter (to be mailed) was placed on the (writing) table an hour (ago), it is certain (will be) there now.
  • A. to be mailed
  • B. writing
  • C. ago
  • D. will be


【正确答案】 D
【答案解析】此句为虚拟语气，考点在于be certain to do sth.。应将Will be改为to be。