Probably 1, however I can see why that would be a tiny bit confusing.
Building walls protects from incoming invaders(at least back in the day), creating armies, makes a force to go and fight to protect the people, and what was the other one? Oh yea, moving to a safer place.
Doing that would mean making invasions less likely, and making your people feel and be safer.
Hope this helps.
Killed an estimated 20 million to 50 million<span> victims.</span>
B. Biosphere (not too sure)
The answer is the second option, pyramids, because if you look at some of the most famous Mayan and Egyptian architectual works, you will see that they both have pyramids, they both might look different, but are used by both.