答案：C

题目分析：句意，我们的目标是构建一个学有所教、劳有所得、病有所医、老有所养、住有所居的和谐社会。定语从句的正常语序是：all people are well educated, workers well paid, patients well treated, elders well tended, and families well accommodated in the society. 定语从句修饰 society, 所以用which，介词in提到了关系代词的前面，关系代词前有介词时，不能that,故选C。

点评：定语从句中关系词都有比较固定的用法，主要看它在定语从句中作什么成分，有时候会把介词提到关系代词的前面。