_______cloning human embryos is not legal in many countries, some scientists are already pushing ahead with research in order to produce a cloned human baby.

A．While

B．When

C．Since

D．if only

物品从生产地到使用地的过程中，根据需要施加包装、分割、计量、分拣、刷标志、栓标签、组装等简单作业的总称是()。

A.流通加工 

B.生产外延加工 

C.生产加工 

D.辅助性加工