听力原文：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.

According to the speaker, small-molecule therapy can be used to ______.

A．replace genes not functioning properly in the body

B．increase the number of genes working properly in the body

C．modify the function of some genes in the body

D．replace genes absent in the body