下列各项属于物流服务外部环境因素带来风险的是( )。

A．自然灾害的发生

B．国内政治形势的变化

C．新法规的颁布实施

D．对服务工作范围界定不明确

E．各方之间的文化差异

Those were the graduate assistants ______ to do the research work in the lab.

A．to whom it was their responsibility

B．whose responsibility there was

C．whose responsibility was

D．of whom with the responsibility