WAS:
1. I was reading my book.
2. My friend was doing his homework.
3. She was the craziest person I ever met.
4. He was playing soccer with his friends.
5. Your answer was very helpful.
WERE:
1. They were at the cinema last sunday.
2. We were playing tennis.
3. You were watching the TV all the night.
4. They were in the restaurant.
5. We were studying yesterday.