By the end of last week, she______in the west of China for two months helping the homeless children.

A．will stay

B．has stayed

C．would stay

D．had stayed

20世纪七八十年代以来，国际贸易发展最重要的特征之一是( )

A．商品贸易的加速发展

B．技术贸易的加速发展

C．技术贸易的萌芽

D．服务贸易的加速发展