单选题 The parents were much kinder to their youngest child than they were to the other,______, of course, made the others jealous.

【正确答案】 A
【答案解析】[解析] 本句缺少一个连接词，用来指代前面整个句子，在从句中作主语，故应选which。that不能引导非限定性定语从句；what不能引导定语从句；who是指代人，不能指代物。