???????????2???????????20? ????,???????????2??20??,??????????(?)?????????????,????????????4????

?????,???????????4?????????????????????

??????????,???????????4??????,???DNA?,????

??:???? “??????????”_????

?? ???????????4?????

????:1???????????:??????????

2????????

3??????????????

4???????

5??????

???????????2???????????20? ????,???????????2??20??,??????????(?)?????????????,????????????4????

?????,???????????4?????????????????????

??????????,???????????4??????,???DNA?,????

??:????