【题目】Many airlines now allow passengers to print their boarding passes online ______ their valuable time.
A.save
B.saving
C.to save
D.saved

【答案】C
【解析】现在很多航班允许乘客在线打印登机牌，以便节约他们宝贵的时间．句中Many airlines now allow passengers to print their boarding passes online是完整的句子结构，后面要用非谓语动词；to save表示目的，要用动词不定式构成目的状语．故选C．