Water Bottles

Question: Two men/women in absolutely identical conditions have two of the exact same water bottles (full of water). An hour passes, and the temperatures of the water inside the bottles are measured. The temperature of one of the bottles is noticeably higher than the temperature of the other. Assuming that the temperature of the setting they were in, as they were both the same, had to do with the change in temperature of the water, why are they different?

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?