Why might the true effectiveness of biofeedback in the treatment of asthma actually be greater than shown?

Peat deposits are found in waterlogged places where dead plant material piles up. when peat is buried, it undergoes compaction. it is subjected to heat and pressure for a long time, and a lot of water is squeezed out during this process. nearly ten vertical feet of original peat material becomes one vertical foot of coal. which of these remains unchanged in the system during the conversion of peat to coal? a) area b) density c) mass d) volume