Question

（NMET1995） Not until all the fish died in the river ____ how serious the pollution was．

A．did the villagers realize　　　 B．the villagers realize

C．the villagers did realize　　　 D．didn't the villagers realize

 

Answer 1

由圖不難看出，該限制酶識(shí)別的堿基序列是GAATTC，切點(diǎn)是G和A之間。