The disease is mainly caused by a lack of a slippery substance in the lungs called surfactant. This substance helps the lungs fill with air and keeps the air sacs from deflating. Surfactant is present when the lungs are fully developed.
https://medlineplus.gov/ency/article/001563.htm
2) cell-tissue-organ-organ system
PLATO answer - become less salty because a greater amount of water would hold the same amount of salt