The most relevant option regarding how CRISPR-Cas9 might be useful in treating diseases like cancer is:
C) CRISPR-Cas9 could remove from patients the genetic mutations that cause a specific cancer before the cancer begins.
This option accurately reflects the potential of CRISPR-Cas9 to target and edit specific genetic mutations that are known to contribute to cancer development, thereby possibly preventing the onset of cancer. The other options, while they touch on important aspects of health and disease, do not directly relate to the gene-editing capabilities of CRISPR-Cas9 in the context of cancer treatment.