客人要求退饭菜，服务员应怎样处理？

Once a reporter receives his assignment from the chief-editor, he has to ______ on his work and tries his best to work on it until the chief-editor ______ it.  [ ]

A. fix his attention; approves  

B. focus; proves of  

C. concentrate; approves of  

D. get down; approves

含胎儿血红蛋白红细胞比成人红细胞的生命周期长。()

明目延龄丸功效与作用

德育手段创新应注意的问题有哪些

为提高安防系统的功能、降低造价，安防产品的（）已经势在必行。

A.功能整合

B.资源共享

C.性能优化

D.参数统一