It is known that water is not an endless resource,  ________can it be made once more,  so we should

save and protect it. [ ]

A. so  

B. as  

C. thus  

D. nor

核心标准中，质量管理体系的业绩改进指南是( )。

A．ISO 9000:2000

B．ISO 9001:2000

C．ISO 9004:2000

D．ISO 9011:2002