--- Do you know the reason _________ pilots turn off the plane’s lights before taking off?

---The practice is for the passengers to adjust to the dark _________ an emergency.

--- Do you know the reason _________ pilots turn off the plane’s lights before taking off?

   ---The practice is for the passengers to adjust to the dark _________ an emergency.

A. why; for fear that                    B. for which; in case of          

C. how; for fear of                      D. that; in case

--- Do you know the reason _________ pilots turn off the plane’s lights before taking off?

---The practice is for the passengers to adjust to the dark _________ an emergency.

A．why; for fear that                  B．for which; in case of

C．how; for fear of                   D．that; in case

--- Do you know the reason _________ pilots turn off the plane’s lights before taking off?
---The practice is for the passengers to adjust to the dark _________ an emergency.