Which of the following examples best illustrates the application of CRISPR-Cas9 technology in modern science?

CRISPR‑Cas9 lets scientists cut DNA at a precise spot and then add or replace a piece of the genome, almost like editing a sentence in a book. The best illustration of this is the use of CRISPR to correct the faulty gene that causes sickle‑cell anemia, where a patient’s own blood cells are edited to produce normal hemoglobin and then re‑introduced into the body. In doing so, the technology shows how a single genetic change can cure a disease that used to be untreatable. This example demonstrates the core idea of CRISPR: a programmable “scissor” that edits genes quickly and accurately, opening doors for medicine and research.