while, before

[Eric0936]

Employees must turn off the lights ___ they leave the office.

A. before
B. while Answer: A

1.I wonder why while can not be put in this blank.
2.What if I want while put in this sentence, then how to revise it.

[Mister Micawber]

1-- It is odd; it requires very specific conditions (all the switches at the door).
2-- It can't be done in a reasonable way. You could use 'on the way out of the office' instead, however.
_________________
Native English teacher at Mister Micawber's

[Eric0936]

Hi Mr.Micawber,

Well, you mean while is usually used in a specific condition, in this case, it is more like a usual habit, so generally, we use after and before to form a clause of normal habits.

Is it right?

[Mister Micawber]

No, that's not what I mean-- 'while' is used only in the case that two events occur simultaneously. 'After' and 'before' order events that are not simultaneous.
_________________
Native English teacher at Mister Micawber's

[Eric0936]

Now I see, at this case why I chose while at my first answer because I would say that way in my country, then you strongly pointed the "simultaneously" out, quiet clear.

Thanks Mr.Micawber.

[Haihao]

The sentence sounds to me trying to say: The last person who leaves the office room must make sure that all the lights are turned off.