Complete the follwing sentence by selectring the correct option.
the breathing rhythm is geneerated in the `overset((i))"______"` and is influenced by variation in levels of `overset((ii))"______"` in the blood.
A. `{:("(i)",(ii)),("medulla",CO_(2)):}`
B. `{:("(i)",(ii)),("medulla",O_(2)):}`
C. `{:("(i)",(ii)),("frontal lobe",CO_(2) and O_(2)):}`
D. `{:("(i)",(ii)),("frontal lobe",CO_(2)):}`