What should you say when a passenger wants to change their reservation and you need to check the availability first？

What should you say when a passenger wants to change their reservation and you need to check the availability first？
A.Please wait a moment while I check the availability.
B.I can't help you.
C.You should have booked better.
D.Come back later.
正确答案：A
试题解析：礼貌地让乘客等待并说明原因，符合服务规范。