1. Так как присутствие в школе к 10:00 обязательно в связи со сдачей ОГЭ, то следует использовать модальный глагол must или оборот have to.
I have to be at school tomorrow by 10:00. We're taking OGE. I will probably take a taxi.
ИЛИ
I must be at school tomorrow by 10:00. We're taking OGE. I will probably take a taxi.
Ответ: I have to be at school tomorrow by 10:00. We're taking OGE. I will probably take a taxi. ИЛИ I must be at school tomorrow by 10:00. We're taking OGE. I will probably take a taxi.