Complete the correct option 9 Someone was taking / took Peter's bag while he was making a phone call.

The correct answer is took.
Explanation: The action of taking the bag happened during another action. The action that happened while the other action was in progress (taking) is the simple past. The action that was ongoing, (making the call) is in the past continuous. So, the action of taking was a completed action and happened while he was doing another activity.