Simplify the following text for a Grade 4 native English-speaking person.
Original: When the north tower collapsed , debris that fell on the nearby 7 World Trade Center ( 7 WTC ) building damaged it and initiated fires .
Simplified: It is believed that because of this damage , a third building , 7 World Trade Center ( 7 WTC ) , fell at 5:20 p.m. , but this is a debated subject .