The MCA Youth has expected more participants to join the trip to the Expo 2010 Shanghai ________ from May1 to October31 this year to explore the world.

A．being held

B．to be held

C．having been held

D．held

铁路局所属机车在局管内限速回送时，由列车调度员发布命令，限挂（）。

A、摘挂列车

B、小运转列车

C、单机运行

D、摘挂列车或单机