【Melissa Lai】評論

因為前面是時間 所以要變成during which 如果前面只是事物, which 就可以了

【Chien-shu Hsu】評論

什麼時候which前面要加介係詞阿"< 有時候可以只用which ，這題卻又變成要加during.....

【Heidi Lin】評論

原句為兩個句子：Concrete operational stage is from ages 7 to 11.Children can conserve and think logically but only with practical aids and they are no longer self-centered during the concrete operational stage(在具體運思期的期間).用which替代the concrete operational stage，因為是"在一段時間內"所以要用"介詞+which"的方式合併兩個句子：Concrete operational stage is from ages 7 to 11, during which Children can conserve and think logically but only with practical aids and they are no longer self-centered...