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Hi

1. I was taking a shower when the telephone rang

2. I was taking a shower when the telephone was ringing

Are both of them OK? Does the first one mean the the phone rang only once?

Thanks
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I was taking a shower when the telephone rang.
This means that during the time you were in the shower, the telephone began to ring. It does not say how long the phone rang, or how many times. This happens all the time!
I was taking a shower when the telephone was ringing.

This is harder to understand. It means that there were two continuous events that happened at the same time. I would interpret it as:

The telephone was ringing when you got in the shower, continued to ring as you continued to take your shower, and also might have been ringing when you finished the shower. .
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Eight times out of ten, the pairing after was/were ---ing is
when + simple past (when the phone rang, when someone knocked on the door, when the curtains caught fire)

and
while + past continuous (while Helen was sewing, while Jack was eating, while they were watching TV)
that is,
when + (interrupting) event; while + (simultaneous) activity.
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'when + continuous' and 'while + simple' are less often heard patterns, but certainly possible:
That's how things were done when I was growing up.
Nero fiddled while Rome burned.
CJ
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Comments  
Thanks for the explanations!!!
1. I was taking a shower when the telephone rang

2. I was taking a shower when the telephone was ringing

Out of the 2 sentences with this context, only #1 is correct.

# 2 grammatically is correct but logically confusing.

It’s possible to have 2 past progressive events going on in a single context, but must be logical to the context. i.e.

A: Were you home last night? I was ringing your door bell for over 5 minutes.

B: Sorry I didn’t hear you. I was cooking dinner in the kitchen when you were ringing at the door.
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 CalifJim's reply was promoted to an answer.
Thanks guys!

As the boy (run) across the road, he (be knock) down by a car.

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