灌流式培养
参考答案：
是把细胞和培养基一起加入生物反应器后，在细胞增长和产物形成过程中，不断地将部分培养液取出，同时又连续不断地补充新的培养液。
—Your colleague's spoken English is quite good, Amy．
— No wonder, as she in the USA for two years．
A．worked
B．has been working
C．had worked
D．has worked
CRH2型200km动车组制动方式采用（）制动方式与电气指令式空气制动方式并用。
