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Shown here is a ( cold, hot, warm ) air balloon. It works on the principle that ( warm air, cool air, dense air ) rises in cooler air. A hot air balloon has three essential parts: the burner, which heats the air; the balloon envelope, which holds the air; and the basket, which carries the ( spaceships, passengers, astronauts ).
The balloon envelop is open from the bottom and the part marked as P is the bottom fabric of the envelope.The characteristic of the envelop should be ( allow heat to escape, water proof, fire -resistant, should be thick amd heavy ).