Why is lack of oxygen dangerous for climbers?

Which enlightenment thinker believed most strongly that women should enjoy the same rights as men?

When children heard an interesting story about a sympathetic and resourceful african-american child, the aim was to provide them with?

Why are the majority of the world's economies mixed? what may happen to the "pure" types of economies (traditional, socialist/command, market capitalist) when they incorporate elements from other economic models?