WHEN or WHILE

time	I	Sunny
8:00	I study
9:00	I was studying	Sunny was eating sth. (start)
Now	I was studying when my room mate ate sth.

When

two action in the past.

1. happened First(8:00)  -- (past continuous)

2. happened next (9:00) -- (simple past)

ex) I was studying in my room (8:00) when (09:00) my room mate come to our room.

while

two actions happened at the same time.

I was studying(8:00) while my room mate (8:00) was eating.

WHEN QUESTION - : for 2 actions in the past.

- first action happened first(8:00)

- second action happened next (9:00)

I was studying at 9:00 when room mate came.

  what            what time         who

(I was studying)-> what were you doing when your room mate came?

(at 9:00) what time were you studying when your room mate came?

(room mate) who come when you studying at 9:00?

While QUESTION - : for 2 actions in the past.

- first action happened first(8:00)

- second action happened next (8:00)

I was studying at 9:00 while my room mate was eating.

  what            what time      who

Q : 

(I was studying) What were you doing while your room mate was eating?

(at 9:00) What time were you studying while your room mate was eating?

(my room mate) who was eating while you were studying at 9:00 ?

simultaneous actions

We were riding a taxi when we saw a chicken store.

Whom you will meet a the airport?

Can you come and pick me up?

1. while <=> when

2. while = at same time.