his
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his
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him（he ，she，his，him，her）选择括号里的Tim does not live with 他的母亲所以是his So he(因为他是男的)sends a letter to his(他是男的)mother once a week and she（母亲是女的）sends him(他的儿子是男的)a letter once a week toohis=他的 her=她的 him=男的 her=女的 he=他 she=她her好像没用到因为句子没有 her son, sends to her，这类句子 除非 Tim does notlive with_his_mother.So_he_sends a letterto__her_ once a week. 否则，你给的句子根本无法用到her