单选题 Attendants on the train treated all the passengers______and made sure they were comfortable during the trip.
【正确答案】 C
【答案解析】解析：空格处需要填入一个副词来修饰动词treated，所以副词(C)courteously(有礼貌地)是正确答案。过去分词和动词(A)，形容词(B)，现在分词和动名词(D)都不能修饰动词。