参考答案：C

解析：
There are two primary ways that genes can be used to treat disease. The first is gene therapy, in which one or more genes are injected into the patient to replace those that are absent or not working properly. This approach has been used to treat heart disease and many forms of cancer. The second way to exploit genes to treat disease is known as small-molecule therapy. In this approach, a small-molecule (that is a drug) is given to the patient to modify the function of one or more genes in the body.

[分析]： 特定信息的找寻和判断。
该段落首先交代基因用于治疗疾病的方式主要有两种，接着具体介绍：一种是gene therapy，另一种就是题干中提到的small-molecule therapy；根据题干要求，定位到相关信息It this approach，a small-molecule(that is a drug)is given to the patient to modify the function of one or more genes in the body即在患者身上使用微分子来改善身体中一种或更多种基因的功能。由此可判断c的说法与原文相符，是正确答案。
[解题关键] 把握表示次序的信号词和分类信息，注意相关内容，有助于正确解题。