To her joy, Della earned first the trust of her students and then of her colleagues. A. t

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A. those
B. one
C. ones
(答案→)D. that
解析：    
试题分析:句意：让她高兴的是，黛拉首先赢得了学生的信任，然后又赢得了同事的信任。those指代上文出现的复数名词，是特指概念；one指代前面出现的单数名词；ones是指代前面的复数名词，是泛指概念；that指代不可数名词，句中被替代词trust是不可数名词，所以答案选D。