It's on the festival occasions the family get together he misses his late father.A. where;

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A. where; that
B. which; when
(答案→)C. when; that
D. that; when
解析：句意：每当过节家人团聚的时候，他就会想念他的父亲。该句为强调句型，被强调部分为on the festival occasions，但该部分后又加上了一个定语从句，先行词是occasions，在定语从句中作时间状语，故用关系副词when引导。故选C。