(A). 20 automatic, movement sensor gun torrents surrounding your location
(B). A solar powered super robot soldier (about 7 feet tall and medium armor) that can kill zombies easily in small numbers
(C). A huge 50 foot tall, 6 inch wide cylinder shaped, smoothed sides, electrified steel wall surrounding your location
(D). A person among you who dresses like Simon Belmont
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This is probably the first question where (logically) there could be more than one answer. However, with this question I'm looking for the very best answer. Let's start off eliminating the obvious worse answer. "D" is not the answer. It would be nice to have Simon Belmont on your side during a zombie attack, but not someone who DRESSES like Simon Belmont.
The second worse answer would be a solar powered super robot soldier that could kill zombies easily in small numbers. If you were to lock yourself in your room and release the soldier to attack the zombies that would work for a while, but after the Zombies break in and the robot follows them the robot would power down. Another observation is that there is 1 robot soldier and 1,000 zombies. The Zombies would easily overpower the robot, tear it apart by the limbs and drag it off somewhere. Keep in mind that this robot is solar powered! What if its not sunny one day or rainy for a couple of days? Regardless of all of this, this option would be good for a while as the the humans use their firearms to pick off any Zombies from their windows and doors (until the ammo runs dry).
The last 2 choices are pretty good choices. They would both work in a zombie apocalypse / attack, but one of these choices have a not so obvious weakness. The other has many strong points. Let's start with the next to best choice (not the answer). Automatic gun torrents are great for a zombie attack of any kind. There are many types of them and many different levels of quality. With 20 gun torrents it's possible to surround the building with them. With a bit of luck the zombies would get wiped out normally...., but there are two weaknesses to this plan. First these particular zombies are smart (basic intelligence) and fast. The zombies would rush the compound and get past the torrents leaving the humans to fend for themselves. The other problem is after maybe 50 or so rounds (bullets) the torrents would have to be reloaded manually (small clip size for these torrents). This would put the humans in danger of being bitten. Once the zombies get past the torrents it's game over. However another option would be for the humans and gun torrents to make a more concentrated perimeter. The humans could stand behind the gun torrents and pick off the zombies that get past with their limited ammo and firearms. This could potentially get rid of 50- 70% of the zombies, but what happens if the gun torrents aren't reloaded in time or the zombies decide to rush the compound only on one side. the other gun torrents would remain inactive and the zombies would get past for sure even if the humans concentrate their fire on one side. This plan would fail. If two answers were combined torrents and the electrified wall that would make the perfect defense. This leaves just one answer.
Yes, the answer is "C" an electrified, 50 foot tall, 6 inch wide, circular steel wall that surrounds your compound. There is only one real weakness of this electrified wall. If the power goes out then the electricity goes too, but will this affect much of any thing? No, it won't. Even with this you have an unclimbable, (smooth) steel (unbreakable) wall. Digging under the wall wouldn't work for 2 reasons. First, the zombies aren't smart enough and second their bodies wouldn't hold up to the trauma of barehanded digging. The zombies would be picked off by the people defending the compound before they could try digging a hole.
The electrified steel wall will fry zombies that come in contact with it. As we know electricity travels, so even if the zombies were to pile up upon each other , the zombie that is continuously being electrified will fry the zombie that touches it. While the wall completely blocks the zombies and also takes them out, the people will snipe the zombies from the roof, shooting them from the 3rd with handguns and standing by on the ground floor just incase the zombies magically jump 50 feet to get over the wall. It's a total victory!