Here are the completed sentences with the verbs in the past continuous tense:
1. My sister bumped into an old friend while she was shopping at the market in town.
2. The children were playing in the garden when they saw a rainbow after the rain.
3. Maria spilled her coffee on her shirt while she was reading a book at the café.
4. We got lost in the maze while we were exploring the botanical garden.
5. Emily discovered a hidden treasure while she was digging in the backyard.
6. The chef burned the cookies in the oven while he was cooking dinner for the guests.
7. Anna sprained her ankle while she was hiking with her friends.
8. Jake accidentally broke the vase while he was playing with his dog in the living room.
9. The students were discussing their project when they heard a loud noise from the next room.
10. Sarah found her lost keys while she was looking for her phone in her bag.
11. Alex was daydreaming in class when he received an unexpected text message.
12. Lisa slipped on the wet floor while she was walking in the kitchen after cleaning.
13. The cat knocked over a glass of water while it was playing on the table.
14. John missed the bus because he was oversleeping after studying late.
15. Julia stumbled upon a rare flower while she was walking in the forest.
16. The firefighters rescued the cat while it was hiding under the porch during the fire.
17. Sam found a lost wallet while he was picking up trash in the park.
18. The baby fell asleep in the car while we were driving to the beach.