21. The CRISPR-Cas9 system is a powerful new technique for gene editing. Which of the following descriptions about the CRISPR-Cas9 system is Not true? (A) CRISPR is a natural immune system occurring in bacteria to prevent attack by virus. (B) Bacterial Cas9 cuts off the viral DNA sequence and destroys the virus. (C) Streptococcus pyogenes produces Cas nuclease. (D) The CRISPR-Cas9 system can identify upto 20 base long sequence in target DNA. (E) The CRISPR-Cas9 system is now deemed a safe method for treating incurable diseases.