题目内容：
Finally, ( ) we are switching to a new coupon-based system, we will be discontinuing the use of customer reward cards. Reassure customers that they can redeem points until the end of the year. Explain to customers that the coupon system will provide greater savings. If a customer has any further questions, please refer him or her to the manager on duty. Thank you for your hard work in recent weeks. Sincerely, Greg
(a) although (b) unless (c) so (d) because
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