All of the new employees receive training packets (that/which ______ details about their duties.)
括號內為形容詞子句, 用來加以說明前面接的training packets(先行詞)
that or which 為關係代名詞
選擇時可將先行詞放回形容詞子句內:
Training packets contain details about their duties. 成為一完整句子無誤時
那就對了!