What should you do if a passenger asks to change their flight to an earlier one， but there are no available seats？

What should you do if a passenger asks to change their flight to an earlier one， but there are no available seats？
A.Sorry， no seats available. You're out of luck.
B.Let me put you on the wait list and inform you if a seat becomes available.
C.You can't change then， end of story.
D.Try again next time.
正确答案：B
试题解析：当乘客要求改签到更早的航班但没有可用座位时，客服人员应将乘客列入候补名单，并告知如果有座位空出会通知乘客。