Misc: What is the white semicircle on a fingernail?

Questions

[pot luck] what name is given to the four weeks before christmas?

[pot luck] in what us state is 'mammoth cave'the longest cave in the world?

[pot luck] which reclusive american millionaire had a phobia about germs?

[pot luck] what purplish colour was the first to be produced synthetically as a dye?

[pot luck] which contains the most calories an avocado or a large potato?