i was walking along the street▁i met a friend of mine .划横线的填什么?

i was walking along the street▁i met a friend of mine .划横线的填什么?
i was walking along the street▁i met a friend of mine .划横线的填什么?

i was walking along the street▁i met a friend of mine .划横线的填什么?
when(突然)