Faced with a bill for $ 10,000, _______.

[      ]

A. John has taken an extra job

B. the boss has given John an extra job

C. an extra job has been taken

D. an extra job has been given to John

制氧流程详细可分为十大系统，即空气压缩系统、（）、换热系统、制冷系统、（）、安全防爆系统、产品压缩输送系统、加温解冻系统、（）、电控系统。