Answer:
The Marburg virus wasn't mutating this early on, therefore the Coronavirus is much more deadlier and almost impossible to get a cure for, due to the rapid change in pathogens!
Years would be the independent variable because any sort of time is usually the independent variable.
I would rather suggest.....4th one as researcher mad hybrid that is flood resistance by selective breeding !!!
Skeletal system.
Without a proper skeleton, we would not have enough rigidity to properly move. We'd be an awkward pile of skin, muscle & bodily fluids.
Hope that helps!
