We are not conscious of the extent of which work provides the psychological satisfaction that can make the difference between a full and empty life.

A．to which

B．in which

C．at which

D．by which

隧道式冷丝机的（）位于振动式输送机工作网面的下方，其作用是将冷风均匀的吹到振动式输送机的工作网面上。