参考答案：A

解析：[分析] 固定搭配 for the sake of是固定搭配，表：“为了”；本句意为：尽管岛上的生活非常艰苦，这个医生为了当地的民众仍留在岛上。for the reason后常跟that从句；in aid of支持，援助；例：raising fund in aid of the sick募捐帮助病人；而the privilege of doing sth．有……的特权/特别待遇，例：Today，we have the privilege of listening to two very unusual men． (今天我们有幸听了两个与众不同之人的讲话)；the privilege to do sth．享有做某事的特权，例：It is a privilege to hear her play．听她的表演是种特别幸运之事；concern关心，担心，担忧，例：The managing director's only concern was how to improve the quality of their products．总经理心里想的全是如何提高产品质量。因此A为答案。