Complete the sentences.use the past continuous and the past simple. I _____ in the park when I_____ my friend.( walk,see).

I was walking in the park when I saw my friend. Joe was running across the road when he fell down. We were having a picnic when suddenly it began to rain. The scientist was working late when he made a discovery. Mrs Johns was shopping in the mall when she lost her bag. The boys were playing football when they broke the window.