Underline the correct form of the verb.e.g. I booked my holiday

Underline the correct form of the verb.
e.g. I booked my holiday ages ago. I AM GOING/will go to Spain

1. Maybe ILL GO/AM GOING to bed early tonight.
2. Look at those black clouds! Its probably GOING TO/WILL rain.
3. I promise I AM GOING/WILL feed the cat.
4. I WILL/AM GOING TO order a pizza if you like.
5. I want to buy a new video game so ILL/M GOING TO save my pocket money.

И ещё надобно объяснить, почему выбран этот грагол
Заранее спасибо!