operation前面加a还是an

前面加an，因为它是元音开头的:

/ˌɒpəˈreɪʃn/

n. 操作经营[外科] 手术[数][计] 运算

The operation saved her life.

手术挽救了她的生命。

Will the operation leave a scar?

手术会不会留下疤痕

Will I need to have an operation ?

我需要动手术吗

There are three ski lifts in operation.

有3辆滑雪缆车在运行。

He's mending slowly after the operation.

手术后，他正在缓慢好转。