— Bob! How is your project? I heard you started it last Friday, right?

— Oh! I_____ for it. But I haven't decided when to do it. [ ]

A. have prepared

B. had prepared

C. have been preparing

D. was preparing

螺杆式空压机吸气滤清器的滤芯经过3次清理或使用多长时间，没有损坏也必须更换。（）

A、5个月

B、6个月

C、7个月