题目内容：
what does the author imply by saying"rewards cards can be a useful option for the savvy consumer"
A． Reward cards are helpful when peopleknow them totally wel B． Reward cards are useful only whenpeople purchase with the
C． The value of the card will vanish frommonth to month in a short tim
D． Rewards cards will serve people withcomfort and convenienc
参考答案：
答案解析：