A passenger wants to upgrade their ticket after purchase. You should：

A passenger wants to upgrade their ticket after purchase. You should：
A.Say it's not allowed.
B.Check the availability of the upgrade and inform the passenger about the additional cost.
C.Upgrade it for free.
D.Charge a hidden fee for the upgrade.
正确答案：B
试题解析：乘客购票后想升舱，客服人员应先检查是否有可升舱的座位，然后告知乘客升舱所需的额外费用。