The procedures(程序) of operating a computer have been ______ several times, the results

of which have made it much easier _______.   [ ]

A. cut down; to operate              

B. simplified; to be operated  

C. reduced; to be operated            

D. simplified; to operate

关于植物组织培养的叙述正确的是[ ]

A．离体的植物器官或细胞培育成愈伤组织

B．愈伤组织培育成植株

C．离体的植物器官、组织或细胞培养成完整植物体

D．愈伤组织形成高度液泡化组织