单选题 (Witnesses) of the crime (find difficult) to explain (why) they (didn't) call the police.
  • A. Witnesses
  • B. find difficult
  • C. why
  • D. didn't


【正确答案】 B
【答案解析】改为find it difficult。it做形式宾语，真正的逻辑宾语是to explain why they didn't call the police。