21. The CRISPR-Cas9 system is a powerful new technique for gene editing. Which ofthe following descriptions about the CRISPR-Cas9 system is Not true?
(A) CRISPR is a natural immune system occurring in bacteria to prevent attackby 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 targetDNA.
(E) The CRISPR-Cas9 system is now deemed a safe method for treatingincurable diseases.