After such fantastic explanations, could you decide which the best option is?
1. They are going to buy / will buy some biscuits this afternoon in case Jean doesn’t have any.
2. Martin is going to do / will do some revision when he gets home. That’s what he said this morning.
3. I am going to leave / will leave home when I’ve saved enough money to get my own flat.
4. I still don’t know what I’m going to do / will do when I leave school.
I hope you’ve learnt a little bit more!