I am afraid I am not fit for the job because it is one requires a lot of patience.A. whoB

问题补充：

I am afraid I am not fit for the job, because it is one requires a lot of patience.

A. who

B. that

C. what

D. where

答案：

A. who

(答案→)B. that

C. what

D. where

解析：关系代词that在引导的限制性定语从句中充当主语，指代one (the job)。故选B。