Simple past or past progressive?

Gap-fill exercise

  
Fill in all the gaps. Then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!
1) While John (to sing) a terrible song, his friend James (to come) into the room.
2) Jane (to look) for a shoe shop, when she (to meet) Sue.
3) Emma (to run) along the street, when she suddenly (to see) an accident.
4) My friend (to call) me, while I (to play) rugby.