They are the first species that could live on dry ground.
Carbon would be the answer to this because it is an element while water is a compound. In addition, carbon had 4 bonding sites which allows it to form a variety of molecules like sugars, proteins, and even DNA that are essential for life as we know it.
Diaphragm...is the muscle that helps in respiration.....there are also some other but....you said flat so diaphragm !
