单选题 While others sat at home studying papers on the subject, Jefferson get into a boat and made ______ observations.
  • A.of-the-spot
  • B.in-the-spot
  • C.on-the-spot
  • D.at-the-spot
【正确答案】 C
【答案解析】[解析] on-the-pot的意思是“立即，当场”其他三个都不是固定搭配。所以，答案是C。