21) ____ on a clear day, far from the city crowds, the mountains give him a sense of infinite peace.　 　A) If walking B) While walking C) Walking D) When one is walking為什么不能選Ｂ

熱心網(wǎng)友

本句的主語是Mountain，如果前面用現(xiàn)在分詞作狀語修飾的話，While后動(dòng)作的發(fā)生者是Mountain而不是he.本題答案應(yīng)該選D