单选题 ______ is a good form of exercise for both young and old.
  • [A] Walking
  • [B] To walk
  • [C] The walk
  • [D] Walk


【正确答案】 A
【答案解析】[A]Walking 动名词做主语，是正确答案。[B]To walk有还没做而将要去完成的意味，不符题意。