Answer:
In the main-idea graphic organizer, one should put the main idea in the middle circle.
In a main-idea graphic organizer, there is a main idea and some supporting details that need to be arranged. Students can customize their main-idea graphic organizers in any form they want -umbrellas, tables, circles, maps, etc.-, always taking into consideration that the main idea should be placed in the middle, and the supporting details below or around, depending on the form.