Which Door?

Question: Suppose you had to pick 1 of 3 doors to go through. One has ninja assassins, one has a lion that hasn't eaten in 3 months, and one has a flaming inferno. Which door should you choose in order to live?

Question: People see through me, but none pass through without killing me. I can be anywhere, and can be seen double or single. What am I?

Question: During what month do people sleep the least?

Question: When is 99 more than 100?

Question: What can be broken but never forgotten?

Question: Surrounded by life , yet life is its biggest enemy. But without life there is no need for it to exist. What is it?