three

丙 depicts a hearth with a burning fire. The original meaning of 丙 was brightness, but such meaning was then replaced by 昺 and 炳. On the other hand, stem of plant is burnable which can be used as firewood, so 丙 also meant stem of plant, such meaning has been replaced by 柄. Now 丙 solely means the third of TianGan after 乙, since a plant will stretch its stem(one of the original meanings of 丙) and grow long after it burgeoned(the picture of 乙).