Which of the following is a reason that Constantinople was able to last as long as it did? Walls
Navy
All of these
Location on a peninsula

I would actually go with all of the above.

Constantinople had a large amount of resources to spend on the navy as well as maintaining the Great Wall of Constantinople. The location being in the peninsula definitely helped as well, since just getting there was a hassle.

Hope that helps, have a good day.

Ithink the answer is a :