Answer:
I think... external force (3)
Step-by-step explanation:
It looks like you're on a test so go with your best judgement here.
I don't know much about this, and I've never seen this in math. Yet, logically speaking, that seems like the best answer here. Again, I don't really know. We can rule out air conditioning and furniture. So our two contendors are external force and weak walls. So think back to your notes hopefully something is in there lol. Good luck.
