Parathyroid hormone and Parathyroid glands
Answer:
Nope.
Explanation:
It is not good for the passengers or the person doing it. For example, vulnerable people like people with asthma, lung problems, respiratory difficulties could be on the train and since it is an enclosed space with no open-able windows or air cracks, it can be very dangerous.
Anyways, the answer is cells. Cells in the reproductive organs (testes and ovaries in humans) divide to form gametes.
Hope this helped :)
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