A common ancestor is evident when comparing of different species in the phylum Chordata, especially in the early stages.

oxygen +1 most likely

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.

i believe your answer would be c.. : )