Cook was a strict but good captain , who , usually , took care of the sailors on his trip

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A. the one
(答案→)B. one
C. that
D. this
解析：考查代词，the one特指前面的可数名词单数，one泛指前面的可数名词，that代指前面的可数名词单数，或是不可数名词，this指代下文，句意是：Cook是严格的但很好的船长，一个通常在航行中照顾水手的船长，one指代a captain。选B。