He (fall) asleep while he (study).
He FELL asleep while he WAS STUDYING.
When I (arrive), they (look) for the lost girl.
When I ARRIVED, they WERE LOOKING for the lost girl.
He (walk) when he (fall).
He WAS WALKING when he FELL.
He (break) his leg while he (play) football.
He BROKE his leg while he WAS PLAYING football.
I (see) my friend while I (shop).
I SAW my friend while I WAS SHOPPING.
We (sail) along the beach when there (be) a storm.
We WERE SAILING along the beach when there WAS a storm.
While they (play) football, they (see) a snake.
While they WERE PLAYING football, they SAW a snake.
She (swim) when a shark (attack) her.
She WAS SWIMMING when a shark ATTACKED her.
He (listen) to music when his teacher (walk) in.
He WAS LISTENING to music when his teacher WALKED in.
He (sleep) when the clock (ring).
He WAS SLEEPING when the clock RANG.
She (cook) dinner when she (cut) her finger.
She WAS COOKING dinner when she CUT her finger.
I (have) an accident when I (drive) home.
I HAD an accident when I WAS DRIVING home.