What word has kst in the middle, in the beginning, and at the end?

What is better than the best thing and worse than the worst thing?

What do you get if you add 2 blackberries and 5 apples?

what has a neck but no head but has arms and stomach?

There are 3 doors On a stranded island. The first one with a weaponed serial killer. The second one with 100 crocodiles. And the 3rd one has a tiger that hasn't eaten in 4 years. Which one is the safest?