This is a difficult and stressful job, but one you can really help people.A. thatB. where

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A. that
(答案→)B. where
C. which
D. of which
解析：考查定语从句。先行词为job，one作job的同位语，同时是后面定语从句的先行词，从句中缺少地点状语，所以用where，相当于in which，故选B。