【题目】 Their youngest girl is at the stage ______ she can say a single word but not a full sentence
A. when B. which C. that D. where
在线课程【答案】D
【解析】
试题分析： 考查定语从句。句意：小女孩现在处于说单个字而不能说完整句子的阶段。the stage是先行词， 定语从句_____ she can say a single word but not a full sentence缺少状语，故选D项。